US President George W Bush said British Prime Minister Gordon Brown should only withdraw forces from Iraq based on conditions on the ground and not an arbitrary timetable.

Bush issued the advice in an interview published on Sunday ahead of his visit to Britain, the final stop of a European farewell tour on which he has won support for ratcheting up pressure on Iran over its nuclear programme.

He told Britain's Observer newspaper that the United States and Britain, Washington's main ally on Iraq, obviously wanted to bring their troops home but that could be done only "based upon success."    

"Our answer is: there should be no definitive timetable," said Bush, adding he was "appreciative" that Brown was in frequent touch about "what he and his military are thinking."    

The newspaper described Bush as issuing a warning to Brown, but the White House dismissed that tone, saying there was no disagreement between the United States and Britain on Iraq. It later released a transcript of the interview as clarification and said Iran was likely to figure more prominently in talks.

Both agreed that any troop reductions would be based on "progress on the ground, on the advice of our military and not according to any arbitrary schedule," Bush national security adviser Stephen Hadley told reporters aboard Air Force One.

"There is no disagreement between us and Prime Minister Brown on this issue," he said.

Only about 4,200 British troops remain in Iraq, most of them stationed at a base in the south. Britain has indicated it could pull them all out by the end of 2008, but with the situation still unstable in Iraq, that appears unfeasible.

After arriving in Britain under heavy guard, Bush and his wife Laura had tea with Queen Elizabeth and toured Windsor Castle ahead of a social dinner with Brown and his wife and bilateral talks on Monday.

Bush was led by the queen who pointed to a squat suit of armour that belonged to Henry the Eighth as well as royal crests covering the ceiling. Bush looked up and nodded as they were trailed by Laura and the queen's husband Prince Philip.

Bush has a more formal relationship with Brown than his  predecessor, Tony Blair, Washington's staunchest supporter over Iraq. Brown is battling against poor opinion poll ratings and Iraq is a divisive issue in Britain.

BBC television showed a small group of protesters in Windsor demonstrating against Bush but were out of his view.

When Brown visited Washington in April he caused a stir by meeting the 2008 presidential candidates before Bush, a sign of how leaders are increasingly looking towards a new president.

The White House was keen to play up the mutual respect of the two men and said they had a lot to discuss, including Iran, climate change, energy policy, and the situation in both Iraq and Afghanistan.

With much of Europe still smarting over the US-led invasion of Iraq, Bush has spent a lot of his trip trying to forge a united front to press Iran to suspend its enrichment of uranium which could be used to build nuclear bombs. - Reuters