Jeremy Renner, Chris Evans and Scarlett Johansson are among the Avengers' all-star cast

It follows on from the hugely successful first movie, reuniting stars including Robert Downey Jr as Iron Man and Chris Hemsworth as Thor.

Marvel villain Ultron is a rebellious artificial intelligence which creates an android that attacks the Avengers.

Whedon revealed the name after footage of the latest Thor film was shown.

The footage was introduced by actor Tom Hiddleston - who played villain Loki in the first Avengers film - in full costume, according to Hollywood Reporter.

Hiddleston stayed in character, making his speech and rallying members of the audience as they chanted the villain's name.

Comic-Con, which has been running since 1970, celebrates "the historic and ongoing contribution of comics to art and culture".

It holds conventions and events featuring comics and related popular artforms - not least films featuring comic-book characters and computer games.

                  Spenser starred in Just William when he was 14

Spenser, who appeared in episodes of Z Cars, Dixon of Dock Green, The Saint and Doctor Who, also directed two 1991 documentaries on comic Benny Hill.

Former head of BBC radio drama John Tydeman said he was "a marvellous radio actor with a very distinctive voice".

Mr Tydeman said Spenser died on Saturday in Spain, where he had lived.

Spenser began his career aged 11 when he worked in plays on Children's Hour, having auditioned for the show's producer Josephine Plummer.

Mr Tydeman said he was then cast in the role of William by its author Richmal Crompton.

Spenser said of the era: "Difficult though it may seem today, radio actors and actresses were considered to be 'stars'. Their voices were as recognisable as faces in Coronation Street today. There was no television."

He added: "Radio was the friend in one's own home, giving one the news in a quiet sensible fashion, and entertaining one with music and zany comedy and drama."

After starring in various TV shows, he played Thonmi in six episodes of Doctor Who with Patrick Troughton.

They were broadcast in 1967, and titled The Abominable Snowmen.

He went on to work as a radio producer, producing plays for the BBC including Anthony Trollope's The Way We Live Now, in 1988, and Mr Norris Changes Trains, based on the Christopher Isherwood novel, in 1984.

His historical drama City of the Horizon, about the Pharaoh Achnaton, was broadcast in 1972 and 1976.

The companies want to be able to report regular statistics about the nature and scope of what data is being asked for.

Whistle-blower Edward Snowden's revelations about US spying capabilities has left the tech firms keen to assert their independence.

Authorities are said to be considering the companies' request.

"We just want to make sure we do it right," said Gen Keith Alexander, director of the National Security Agency.

"We don't impact anything ongoing with the FBI. I think that's the reasonable approach."

The companies sent a letter outlining their request on Thursday to Gen Alexander, as well as President Obama and Congress.

It was co-signed by some of the most influential companies in the tech world, including Facebook, Twitter and LinkedIn.

Campaign groups such as the Electronic Frontier Foundation and Human Rights Watch are also backing the action.

Companies are currently allowed to release limited data regarding security requests and their nature.

But as it stands those disclosures must be limited in scope, and in many cases require that the firms ask the courts for permission to make the information public.

Many users of popular services, particularly social networks, reacted angrily to the news that companies regularly make available information about users when requested to do so.

"They don't have a choice. Court order, they have to do this," Mr Alexander from the NSA said, suggesting that security authorities could be open to the idea.

"What they want is the rest of the world to know that we're not reading all of that email, so they want to give out the numbers.

"I think there's some logic in doing that."

Prosecutors will test measures on Apple's iPhone 5 and Samsung's Galaxy S4 to measure effectiveness against common tactics used by thieves.

Various cities across the world have called on manufacturers to do more to deter phone theft.

London Mayor Boris Johnson has written to firms saying they must "take this issue seriously".

In a letter to Apple, Samsung, Google and other mobile makers, Mr Johnson wrote: "If we are to deter theft and help prevent crimes that victimise your customers and the residents and visitors to our city, we need meaningful engagement from business and a clear demonstration that your company is serious about your corporate responsibility to help solve this problem."

Prosecutors in the US are following a similar line - last month meeting representatives from the technology firms to discuss the matter.

They are calling for a "kill switch", a method of rendering a handset completely useless if it is stolen, rendering a theft pointless.

Statistics from the US Federal Trade Commission suggest that almost one in three robberies nationwide involves the theft of a mobile phone.

In New York, 40% of robberies are phone thefts - a crime so common it has been dubbed "Apple-picking" by police.

London has seen a "troubling" rise in mobile phone theft, the mayor's office said, with 75% of all "theft from person" offences involving a phone - 10,000 handsets a month.

Close scrutiny

The firms have offered theft solutions to help combat the problem.

Apple's Activation Lock - which will be part of the next major iPhone and iPad software update - is to come under close scrutiny.

Thieves will often deactivate a phone immediately to stop it being tracked after a theft. Activation Lock is designed to make it harder to then reactivate, as it requires the entry of the log-in details used to register the phone originally.

For Samsung and other handsets, prosecutors, aided by security professionals, will be testing theft recovery system Lojack.

"We are not going to take them at their word," the prosecutors in New York and San Francisco said in a joint statement.

"Today we will assess the solutions they are proposing and see if they stand up to the tactics commonly employed by thieves."

Disney Infinity encourages players to collect additional figures and add-ons inspired by the company's films.

The starter pack, with three figures, will cost around £60, with an optional 17 extra figures costing around £12 each.

Disney told the BBC the game represented good value for parents, and that toys could be easily swapped.

Lead producer John Day said: "I think the value proposition here is really quite good because normally, when Disney releases a new film, there would be another game associated with that that would be upwards of £50.

"But with Infinity we can still deliver that additional content moving forward, and for these playset packs - which are, in their own right, an entire game - the recommended retail price is going to be closer to £30.

"So you can actually get £50 worth of stuff at a substantial discount."

The game, which will be released on PlayStation 3, Xbox 360, Wii, Wii U and Nintendo DS next month, is designed to be continually upgraded as new characters become available - either from previous films made by Disney, or upcoming titles.

The starter pack contains the game's core accessory, a docking station for figurines and other add-ons which can be swapped while the game is being played, changing characters and environments instantly.

The figures contain RFID chips - tiny, low-cost components that can contain a small amount of data.

Disney Infinity will launch with 20 different characters available to buy - with more being added at a later date.

As well as the figures, gamers can also buy £4 add-on packs containing discs that can make characters stronger and quicker, or change other areas of the game.

Siobhan Freegard, founder of parenting advice site Netmums, said there would be concerns over the potential for pester power.

"I do worry that at the moment so many parents are strapped for cash," she told the BBC.

"It's not a cheap present - and to go back to school and find Little Johnny down the road has all the characters will make it hard. It is a never-ending thing. Parents need to know what they're signing up to."

On the subject of the add-on packs, she added: "I'm not sure I like that your character can be better because your parents have more money."

'Immediate pull'

The Disney Infinity concept borrows heavily from Skylanders, a massively successful game that has over 100 additional characters that can be added for around a similar price.

However, Ms Freegard said children's immediate familiarity and fondness for the Disney characters might mean there was higher demand.

"The thing about Skylanders is that the children for a long time don't know the characters," she added.

"But parents will buy this, and children will already know the names of all the others [Disney characters] - there's an immediate pull."

Beyond the tradeable figures - which are interchangeable with different platforms, meaning a PS3-owning child can swap their characters with a friend who has an Xbox 360 - the game's key selling point is the ability to create worlds in its "toybox" mode.

"I'm very excited about the educational prospects of this," said Disney's Mr Day.

"I have two boys, ages two and four, and I like the idea that they can be learning about how to do logical connections using the toys in the Toybox.

"We can bring in toys like buttons and doorways, and you can connect the button to the doorway and have the button open the door when you step on it.

"It seems very basic, but at the same time we're talking about logical inputs and outputs. It really is a lightweight programming language."

Juan Manuel Santos also ordered more troops to the eastern Arauca region, where the attack by suspected Farc gunmen took place on Saturday.

Bogota and the Farc are currently holding talks in Cuba to end more than five decades of conflict.

The government has rejected a rebel call for a truce during the talks.

It says a ceasefire would only provide the opportunity for the left-wing rebels to regroup and rearm.

"I instructed our forces not to stop shooting until the conflict is over," said Mr Santos, who is now in the Arauca region for a security summit in the town of Tame.

"These attacks are not the way. They will be confronted forcefully.

"All of Colombia must work for peace precisely so that incidents like those that occurred in the last 24 hours never happen again," he said adding that the peace talks in Cuba should continue as normal.

The incident happened in a rural part of Arauca known as El Mordisco, when more than 70 Farc rebels attacked a group of 26 soldiers guarding an oil pipeline.

The Colombian authorities said 15 government soldiers died in the attack, although earlier report had put number of the killed at 17.

Six rebels were reported to have died and another 12 seized by the army.

In a separate incident in south-west Colombia, clashes killed four soldiers and several Farc fighters.

The peace talks, which started in November, represent the fourth attempt at a negotiated peace deal since the beginning of the conflict in the early 1960s.

The last attempt to achieve peace collapsed in 2002, when it became clear that the rebels had become stronger during more three years of negotiations under a ceasefire.

Meanwhile, the Farc said it had captured a former US soldier and was willing to release him to prove its commitment to the peace process.

In a statement, the rebels named the man as Kevin Scott Sutay and said he had been taken on 20 June in El Retorno in the southern Guaviare Department.

The US has denied he was on any form of military operation, saying he was in the area as a tourist and had "nothing to do with Colombia's internal conflict".

The Farc are thought to have some 8,000 fighters, down from about 16,000 in 2001.

The government estimates that 600,000 people have been killed since the conflict began with some three million more internally displaced by the fighting.

Last week, the Farc's chief peace negotiator said the conflict was nearing its end.

Ivan Marquez, who is taking part in the Cuba talks, called on left-wing parties and unions to join the effort to achieve peace.

The government wants to sign a peace accord by November. But Mr Marquez warned against rushing into a settlement.

The pontiff will be greeted by some two million young people from all over the world at the Roman Catholic World Youth Day festival in Rio de Janeiro.

The first Latin American Pope will also celebrate Mass on the famous Copacabana beach and visit shanty towns.

Some 22,000 security staff will be on duty during the visit of the Pope, who is not using his armoured Popemobile.

Ahead of his week-long trip, the 76-year-old Pope from Argentina called on his followers to join him spiritually on his journey through prayer.

The pontiff is due to arrive in Brazil - the world's most populous Catholic country - later on Monday, and huge crowds are expected to greet him at Rio airport.

The Vatican says it has full confidence in the ability of Brazilian security forces to protect the pontiff during his visit.

However, Pope Francis' direct style of communication, his desire for close proximity with his flock and his frequent rejection of protocol are creating some worry among the organisers of the visit, the BBC's David Willey in Rome reports.

In Rio, the security forces have set up several monitoring centres to keep a close eye on the Pope's every step.

The pontiff will also be using army helicopters to avoid Rio's heavy traffic jams.

The Brazilian authorities earlier banned masks at Pope Francis's opening Mass at the World Youth Day.

They are worried that the visit could spark a repeat of June's unrest, when many wore masks in the crowds.

There were widespread anti-government protests last month during the football Confederations Cup. Many of the protesters were wearing Guy Fawkes masks, which have become a feature of demonstrations around the world.

The demonstrators have taken to the streets to complain about the state of public services such as transport, health and education and about what they perceive as the inefficiency of their politicians.

The two planes jettisoned four bombs - two inert and two unarmed - in more than 50m (165 ft) of water, away from coral, to minimise damage to the World Heritage Site, the US navy said.

The jets were to bomb an island range nearby, but the mission was aborted.

The AV-8B Harriers were low on fuel and could not land loaded, the navy added.

The incident happened during the training exercise Talisman Saber, involving US and Australian military personnel.

The two jets had been instructed to target the bombing range on Townshend Island.

However, the mission was aborted when hazards were reported in the area.

"It was not safe to drop the bombs. There were civilian boats right below them," Commander William Marks of the US Seventh Fleet told ABC radio.

The planes then dropped the bombs in the marine park off the coast of Queensland. None of the devices exploded.

The bombs - each weighing 225kg (500lbs) - do not pose a hazard to shipping, the US Navy says, and charts are to be updated to show the unexploded ordnance.

"There is minimal environmental impact," said Cmdr Marks. "It is a safe situation for the environment, for shipping, for navigation."

However, the US Navy said it was open to the idea of recovering the bombs from the seabed.

"If the [Great Barrier Reef] park service and the government agencies of Australia determine that they want those recovered, then we will coordinate with them on that recovery process," said Seventh Fleet spokesman Lt David Levy.

The Great Barrier Reef is the world's largest coral structure rich in marine life.

It stretches for more than 2,600km (1,680 miles) along Australia's eastern coast.

The earthquake near Dingxi city had a magnitude of 5.98 and was shallow, with a depth of just 9.8 km (6 miles), according to the US Geological Survey.

Dingxi local authorities say many houses have collapsed in the quake.

In 2008, an earthquake in Sichuan province left up to 90,000 people dead and millions homeless.

At least 47 people had been killed, reports from China's national radio and Agence-France Presse news agency citing local officials said.

Another 296 other people were injured, the Dingxi local government said on its official Sina Weibo microblog.

In Gansu's Zhangxian county, at least 5,600 houses were seriously damaged and 380 collapsed, while some areas suffered from power cuts or mobile communications being disrupted, the Earthquake Administration of Gansu province said.

Crews of fire fighters and rescue dogs have already arrived at the scene, the BBC's Celia Hatton in Beijing reports.

The closer to the surface an earthquake strikes, the more damage it can cause, our correspondent adds.

The earthquake reportedly triggered a series of mudslides and landslides, state-run news agency Xinhua reported.

The Gansu military police has deployed 500 soldiers, including 120 specialist rescuers, while 500 emergency tents and 2,000 quilts are also being transported to affected areas, Xinhua added.

Officials from the civil affairs, transportation and earthquake departments are also visiting local towns to assess the damage, a statement on the Dingxi party website said.

"You could see the chandeliers wobble and the windows vibrating and making noise, but there aren't any cracks in the walls," AFP quoted a clerk at Wuyang Hotel, about 40 km (25 miles) from the epicentre, as saying.

"Shop assistants all poured out onto the streets when the shaking began," the clerk said.

The 6.5-magnitude tremor was centred 35 miles (57 km) off the coast south of the capital at a depth of 6.3 miles, said the US Geological Survey.

But while some structural damage and power cuts were reported, officials said there was no risk of a tsunami.

The quake hit at 17:09 (05:09 GMT) and was felt as far north as Auckland.

It smashed windows, knocked stock off shop shelves and burst some water pipes, but there have been no reports of serious casualties.

Wellington resident James Mclaren said the earthquake had caused power cuts in the city suburbs and prompted the temporary closure of its airport.

"There's been a bit of structural damage, lots of shattered glass everywhere," he told the BBC. "Initially there were a few screams and panic, people thought it was another Christchurch."

A 6.3-magnitude earthquake centred near Christchurch in February 2011 killed 185 people.

Sunday's tremor was the latest in a series that have shaken the lower half of New Zealand's North Island in recent days.

New Zealand lies on the notorious Ring of Fire, the line of frequent quakes and volcanic eruptions that circles virtually the entire Pacific rim.

The country experiences more than 14,000 earthquakes a year, of which only around 20 have a magnitude in excess of 5.0.

Satellite images of Africa's Congo Basin reveal that deforestation has fallen by about a third since 2000.

Researchers believe this is partly because of a focus on mining and oil rather than commercial agriculture, where swathes of forest are cleared.

The work is published in the Philosophical Transactions of the Royal Society B.

It is part of a series that is examining the state of Africa's forests.

Dr Simon Lewis, from the University of Leeds and University College London, said: "Most of the focus has been on the Amazon and on South East Asian tropical rainforests, and a big bit of the missing picture is what is going on the Congo Basin in Central Africa.

"We really wanted to pull together information about this amazing region that we know very little about."

Bigger trees

Sprawling across the heart of Africa, the Congo Basin rainforest is second only to the Amazon in size. It covers nearly 2 million sq km (800,000 sq miles).

This latest study reveals that it is in far better health than expected.

Images taken from space allowed researchers to track how the dense foliage was changing over time.

They found that during the 1990s nearly 3,000 sq km (1,000 sq miles) of forest were being felled each year.

But from 2000 to 2010, the rate of deforestation had slowed. Fewer than 2,000 sq km (700 sq miles) of rainforest were lost every year.

"The results were surprising," Dr Lewis told BBC News.

"This is partly because there is a network of protected areas. But it is also because of a lack of expansion from agriculture, and the way these [central African] countries have organised their economies.

"They are very dependent on oil sales and also minerals from mining, and they are investing in that and not investing so much in agricultural expansion."

Another study published in the same journal highlighted the differences between trees in the Congo Basin and those found elsewhere around the world.

Measurements of 130,000 trees show that African species were on average much larger in stature than those in the Amazon. As a result, scientists believe that the Congo Basin stores more carbon, acting as a carbon sink.

Losing parts of the rainforest would have an impact on climate change, biodiversity and the communities that depend on the environment, said Dr Lewis.

He said that Africa's rainforest was at a pivotal point.

Logging could continue to fall because of schemes such as the United Nations' Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD) that offer financial incentives to keep forests intact.

"But on the other side, the big increase in human population and the rise in living standards globally means we may need more agricultural commodities... It could go the other way and go much more like South East Asia or the Amazon and see the expansion of commercial agriculture," explained Dr Lewis.

A statement issued earlier supports the automatic exchange of tax information between countries.

It also backs plans by the Organisation for Economic Cooperation and Development to stop firms moving their profits across borders to avoid taxes.

The OECD said some firms "abuse" current rules to avoid tax.

UK Chancellor George Osborne said the announcement, which came after a two-day G20 meeting in Moscow, was an "important step towards a global tax system that is fair and fit for purpose for the modern economy".

Last month, the G8 group of leading economies agreed a deal to "fight the scourge of tax evasion", and nations including the UK, France, Germany, the USA and Australia are taking part in a pilot information exchange scheme.

British Prime Minister David Cameron made the issue a priority for the UK's presidency of the G8 this year, and Australia has agreed to do the same during its G20 presidency next year.

The OECD said current tax rules, some dating to the 1920s, were created to avoid "double taxation" of companies working in more than one country - but it said they were being abused to allow "double non-taxation".

BBC business correspondent Joe Lynam said the "bandwagon of clamping down on aggressive tax avoidance" was moving on from developed economies to emerging ones like Brazil and India.

The rules should mean bigger bills for companies which could previously "pit one country off against another in terms of tax", our correspondent added.

The G20 asked the OECD to come up with a plan to improve tax cooperation, and the finance ministers said they "fully endorse the OECD proposal for a truly global model" of information sharing.

Their statement called on all countries to make automatic information sharing a reality "without further delay", adding that "capacity-building support" would be provided for poorer nations.

Closing loopholes

The G20 said the changes should be in place within two years, but our correspondent called that "very ambitious" because hundreds of tax treaties exist between countries and "thousands of amendments" might be needed.

Many multinational firms currently avoid tax - legally - by means including loopholes and tax havens, but the new rules could require them to pay more in the countries where they do business.

Firms including Google, Starbucks, Amazon and Apple have been criticised for the amount of tax they pay.

Earlier this year, MPs attacked Google for routing £3.2bn of UK sales through Dublin and paying little tax as a result.

Starbucks has been questioned for transferring money to a Dutch sister company in royalty payments, though the firm agreed to pay more tax after strong public criticism.

The companies point out that these schemes are legal and they have a duty to shareholders to minimise their tax bills.

The UK prime minister told the BBC there was a "stalemate" on the ground, but work must continue internationally to try to find a solution.

UK military chiefs have warned of the risks of arming rebel groups.

Mr Cameron said there was "too much extremism" among the opposition, but moderate groups still deserved support.

Syrian government forces have taken the initiative in recent months, and have been bolstered by the capture of the strategically important town of Qusair in the west of the country in June.

Most of the much bigger city of Homs has been recaptured by government troops backed by Lebanon's Hezbollah.

Washington and London have been looking at ways to increase logistical support for opposition groups and the UK announced last week it was sending £650,000-worth of protective clothing to guard them against chemical and biological attacks.

But reports have suggested support for supplying weapons to rebel groups is receding, due to strong political opposition and widespread concerns about arms falling into the wrong hands.

Mr Cameron told the Andrew Marr show that President Bashar al-Assad was an "evil" man who was doing "terrible things to his people".

But he also said the UK "should have nothing to do" with elements of the opposition also reported to have committed atrocities.

"It is a very depressing picture and it is a picture which is on the wrong trajectory," he said of the conflict.

"There is too much extremism among the rebels. There is also still appalling behaviour from this dreadful regime using chemical weapons. There is an enormous overspill of problems into neighbouring countries."

He added: "I think he [Assad] may be stronger than he was a few months ago but I'd still describe the situation as a stalemate."

'Head in sand'

Despite the UK's concerns about the actions and views of some opposition groups, Mr Cameron said the UK had a duty to support those pushing for a "democratic, free and pluralistic" country.

"You do have problems with part of the opposition which is extreme, that we should have nothing to do with. But that is not a reason for pulling up the drawbridge, putting our head in the sand and doing nothing.

"What we should be doing is working with international partners to help the millions of Syrians who want to have a free democratic Syria, who want to see that country have some form of success."

Mr Cameron also said reports in the media that his wife had been a strong influence on his policy were a "total urban myth".

Samantha Cameron visited a refugee camp in Lebanon in March in her role as ambassador for Save The Children, in which she met families and children displaced by the conflict.

It has been suggested that she has since pressed for a stronger humanitarian response.

The UN says the refugee crisis is the worst for 20 years, with 1.7 million forced to seek shelter in neighbouring countries and an average of 6,000 people fleeing every day this year.

Mr Cameron said his wife had been "very moved" by what she had seen and heard from people who had lost loved ones and whose communities had been destroyed.

But he added: "She does not influence my policy on this. I have been very passionate about this for a long time."

The UK prime minister told the BBC there was a "stalemate" on the ground, but work must continue internationally to try to find a solution.

UK military chiefs have warned of the risks of arming rebel groups.

Mr Cameron said there was "too much extremism" among the opposition, but moderate groups still deserved support.

Syrian government forces have taken the initiative in recent months, and have been bolstered by the capture of the strategically important town of Qusair in the west of the country in June.

Most of the much bigger city of Homs has been recaptured by government troops backed by Lebanon's Hezbollah.

Washington and London have been looking at ways to increase logistical support for opposition groups and the UK announced last week it was sending £650,000-worth of protective clothing to guard them against chemical and biological attacks.

But reports have suggested support for supplying weapons to rebel groups is receding, due to strong political opposition and widespread concerns about arms falling into the wrong hands.

Mr Cameron told the Andrew Marr show that President Bashar al-Assad was an "evil" man who was doing "terrible things to his people".

But he also said the UK "should have nothing to do" with elements of the opposition also reported to have committed atrocities.

"It is a very depressing picture and it is a picture which is on the wrong trajectory," he said of the conflict.

"There is too much extremism among the rebels. There is also still appalling behaviour from this dreadful regime using chemical weapons. There is an enormous overspill of problems into neighbouring countries."

He added: "I think he [Assad] may be stronger than he was a few months ago but I'd still describe the situation as a stalemate."

'Head in sand'

Despite the UK's concerns about the actions and views of some opposition groups, Mr Cameron said the UK had a duty to support those pushing for a "democratic, free and pluralistic" country.

"You do have problems with part of the opposition which is extreme, that we should have nothing to do with. But that is not a reason for pulling up the drawbridge, putting our head in the sand and doing nothing.

"What we should be doing is working with international partners to help the millions of Syrians who want to have a free democratic Syria, who want to see that country have some form of success."

Mr Cameron also said reports in the media that his wife had been a strong influence on his policy were a "total urban myth".

Samantha Cameron visited a refugee camp in Lebanon in March in her role as ambassador for Save The Children, in which she met families and children displaced by the conflict.

It has been suggested that she has since pressed for a stronger humanitarian response.

The UN says the refugee crisis is the worst for 20 years, with 1.7 million forced to seek shelter in neighbouring countries and an average of 6,000 people fleeing every day this year.

Mr Cameron said his wife had been "very moved" by what she had seen and heard from people who had lost loved ones and whose communities had been destroyed.

But he added: "She does not influence my policy on this. I have been very passionate about this for a long time."