President George Bush attempted to pour cold water over Prime Minsiter Gordon Brown's plans to withdraw UK troops from Iraq by warning a lot of 'hard work' still remained.
The US president said western troops should only think of pulling out once they had completed the 'hard work' of defeating al Qaeda and Iranian-backed rebels.
"We need all our coalition partners.
"I understand that everybody's got their own internal politics.
"My only point is that whether it be Afghanistan or Iraq, we've got more work to do," he said.
Mr Bush's remarks, in an interview with Sky News, were his first public reaction to the clearest message yet from Britain that it intends to start withdrawing its 5,500 soldiers based in southern Iraq.
Downing Street and Foreign Secretary David Miliband made clear this week that any decision about a pull-out of British troops would be made on the basis of local conditions in Basra - regardless of the plight of US forces in Baghdad.
The new position is in stark contrast to Tony Blair's and follows a clear change of tone when Mr Brown met Mr Bush this summer.
It is expected that the Prime Minister will announce in October that British forces will hand over control of security to Iraqi troops and police across the whole of southern Iraq.
British troops will switch to 'overwatching status', monitoring their Iraqi counterparts but with reduced numbers - allowing soldiers to come home ahead of a possible general election.
But Mr Bush today made plain that he wanted to pursue his strategy of a 'surge' in troops and wanted allies to stay the course.
He spoke after US general David Petraeus, in charge of operations in Iraq - and due on 12 September to report on the effectiveness of the recent increase in US numbers - warned Australia not to go ahead with plans for a swift troop withdrawal.
Mr Bush widened this warning to include all the allies, saying: "What matters is success and I believe we can be successful.
"This hard work will achieve what we all want, which is over time fewer troops and peace.
"The main thing we want is to make sure that we deal these radicals and extremists a major blow, which is success in Iraq."