US presidential hopeful John McCain has held Downing Street talks with Prime Minister Gordon Brown.

The situation in Iraq was high on the agenda on the fifth anniversary of the invasion and the pair also discussed Afghanistan, climate change and global financial turmoil.

Mr McCain acknowledged the "frustration" of British public opinion at the slow progress of military operations in Iraq and Afghanistan but praised the "long service and sacrifice" of the British forces in the two countries.

He said he was strongly committed to the US operation in Iraq but added that it was a matter for the British Government how long the UK maintained troops there.

"I believe that that decision is made by the British Government and people," he said.

"We appreciate enormously the long service and sacrifice of the British servicemen and women in the military, both in Iraq and Afghanistan.

"I fully appreciate that British public opinion has been frustrated by sometimes our lack of progress in both areas.

"All I can do is express my gratitude to the British Government and people, especially the brave young people who are serving."

Mr McCain reaffirmed his belief that the US troop "surge" in Iraq had proved a success but he warned that there was still more to be done in restoring security.

"Al-Qaeda is on the run. They are not defeated. We're going to have to continue training the Iraqi military and do what we have been doing if we are going to achieve a stable situation in Iraq," he said.

Mr McCain - who stressed that he was visiting as a member of the Senate Armed Services Committee - praised Mr Brown as a strong supporter

"I appreciate very much his commitment to the continued, unique relationship between our two countries which will remain unique. I am a great admirer of the Prime Minister as well," he said.

Mr McCain, a Republican senator who will take on Barack Obama or Hillary Clinton in the race for the White House this year, is also having talks with Tory leader David Cameron.

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