The Prime Minister of Iraq will meet President Bush at the White House today, amid growing unease in Washington over the invasion and the continued presence of US soldiers in Iraq.

Ibrahim al-Jaafari arrived in Washington yesterday and visited wounded American soldiers at the Walter Reed Army Medical Center. Today he will meet Mr Bush at what the White House has described as "a critical time".

"The President looks forward to welcoming Prime Minister Jaafari," said Scott McClellan, the White House press secretary. "This meeting does come at a critical time in Iraq's historic transformation."

The visit of the Iraqi Prime Minister coincides with growing rows in Washington over the initial causes and planning of the war, set off in part by a British intelligence memo published in The Sunday Times and on Times Online.

Known as the Downing Street Memo, the document is a set of minutes from a top-secret meeting in Downing Street on July 23, 2002, which says that American "intelligence and facts were being fixed around the policy" of invading Iraq.

The authenticity of the minutes, which neither the White House nor Downing Street have disputed, has provided American politicians opposed to the war with what they say is proof that the Bush Administration decided to invade Iraq, even though there was no credible threat from Saddam Hussein.

John Conyers, a Democratic Congressman from Michigan, said the memo, which relates a briefing given by C, the head of MI6, show that Mr Bush overstepped his powers as President.

"It goes back to article one, section eight of the constitution that says only Congress has the power to declare war," Congressman Conyers told BBC Radio 4's Today programme this morning.

Congressman Conyers and other Democratic politicians have already held informal meetings in the Capitol about the minutes and plan to present a petition to the White House.

The memos have also prompted a grass roots campaign to increase their visibility, with protest groups printing t-shirts and reprinting the minutes on websites and blogs.

John Aravosis, an anti-war activist told the BBC: "The Downing Street memos are terribly important because it is the first concrete smoking gun we've had. We've got the head of British intelligence telling us that the Bush Administration was lying to the American public. That's monumental."

As approval ratings fall, the Bush Administration is under increasing pressure from Democratic politicians to set a timetable for American withdrawal from Iraq. In the last few days, American military deaths in Iraq reached 1,700 since the war started in March 2003.

Yesterday Defence Secretary Donald Rumsfeld resisted calls for a timetable of withdrawal, telling a Senate Committee it would a "lifeline" for terrorists. "Some in Congress have suggested that deadlines be set for withdrawal. That would be a terrible mistake. It would throw a lifeline to terrorists who in recent months have suffered significant losses in casualties, been denied havens, and suffered weakened popular support," he told the Armed Services Committee.

Vice President Dick Cheney claimed recently that the security situation is improving in Iraq, and that the insurgency was "in its last throes". But last night the top US military commander in the region, General John Abizaid, told the same committee that the insurgency had not diminished noticeably in the last six months.

"There’s a lot of work to be done against the insurgency," said General Abizaid.

"I believe there are more foreign fighters coming into Iraq than there were six months ago. I’m sure you’ll forgive me from criticising the vice president."

An Associated Press-Ipsos poll this month found just 41 percent of Americans supported President Bush's handling of the war -- the lowest that figure has ever been.

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