US presidential candidate Barack Obama has said he is committed to increasing the number of troops in Afghanistan.

Mr Obama was speaking in London following a meeting with British Prime Minister Gordon Brown.

He added that he would like to see the burden of the US military involvement in Afghanistan shared.

London was the final stop on Senator Obama's tour of Europe and the Middle East, which is designed to portray the presidential candidate as a potential world leader.

At Downing Street, he held talks with Mr Brown for almost two hours on a range of subjects including climate change and the Middle East.

Senator Obama said afterwards that the US was grateful for Britain's military contribution in Afghanistan.

He has called for a new partnership between the US and Europe would include a greater European commitment in Afghanistan.

Senator Obama has also been meeting Tony Blair, who is now a Middle East peace envoy, and Conservative leader David Cameron.

The visit is compared to his stopover in Berlin where 200,000 people turned up to hear his keynote speech calling for a renewed partnership between Europe and the US.

Senator Obama's talks at Downing Street were similar to Republican candidate John McCain's visit last March. There was no joint news conference with Mr Brown.

Bin Laden should face Nuremberg-style trial - McCain

Mr McCain has, meanwhile, said that he would favour a trial for al-Qaeda leader Osama bin Laden in the fashion of the Nuremburg trials for Nazi leaders held after World War II.

Asked on CNN what he would do with bin Laden if the mastermind of the 11 September attacks on the US - who is believed to be hiding in Pakistan - is ever caught, the Republican senator replied, 'Of course you put him on trial'.

'There are ample precedents for that. And it might be a good thing to reveal to the world the enormity of this guy's crimes and his intentions,' Mr McCain said.

'We have various options, but the Nuremburg trials are certainly an example of the kind of tribunal that we could move forward with.

'I don't think we would have any difficulty devising an internationally-supported mechanism that would mete out justice,' he said.