British Prime Minister Tony Blair held a telephone conversation with President Bush on Friday in which the two allies reaffirmed their commitment to disarming Iraq, by force if necessary, Downing Street said.
Mr Blair has remained firmly on Mr Bush's side as France, Russia and China, veto-holding members of the Security Council, and key European ally Germany, have voiced strong opposition to a rush to war.
"Both remain agreed that Saddam Hussein has to be disarmed, that he has been offered a peaceful way to do that, but if he fails to comply, cooperate fully and disarm his weapons of mass destruction, then he will have to be disarmed by force," Mr Blair's spokesman said this afternoon.
He said the purpose of the lengthy call was to co-ordinate transatlantic strategy ahead of Monday's progress report to the Security Council by UN weapons inspectors, which could begin a countdown to a US invasion.
Bush, who insists Iraq is hiding banned weapons of mass destruction, is expected to raise the pressure on Saddam in his State of the Union address on Tuesday and meet Blair at Camp David on Friday.
The United States has already committed thousands of troops and hundreds of tanks and bombers to the Gulf, while Britain has dispatched a large naval task force and pledged 30,000 troops.
However, The Washington Post reported on Saturday that the Bush administration, under pressure from allies abroad and Democrats at home not to hasten into war, was expected to let UN inspections go on for several more weeks at least.
A group of anti-war protesters is to set off from London today on their way across continental Europe by bus to Baghdad to offer themselves as human shields in the hope of preventing a military strike against Saddam.