An influential Democratic congressman - who voted for the Iraq invasion in 2003 - has called for the immediate withdrawal of US forces from Iraq.
Mr Murtha is a leading Democratic spokesman on defence issues
John Murtha - a decorated Vietnam War veteran - said US troops had become "a catalyst for violence" in Iraq.
His comments followed attacks from the Bush administration on critics of its Iraq war policy and its handling of intelligence to invade Iraq.
Vice-President Dick Cheney said critics were spreading "cynical falsehoods".
"Our troops have become the primary target of the insurgency, they are united against US forces, and we have become a catalyst for violence," Mr Murtha said at an emotional news conference in Washington.
"US troops are the common enemy of the Sunnis, the Saddamists, and the foreign jihadists... I believe we need to turn Iraq over to the Iraqis," he said.
Mr Murtha - who is a member of a key House of Representatives panel that oversees defence spending - urged the White House to "immediately redeploy US troops consistent with the safety of US forces".
The congressman from Pennsylvania also said a "quick reaction force" should be created in the Middle East.
Mr Murtha's remarks have dealt a further blow to the Bush administration's attempt to rally support for the war in Iraq, the BBC's Justin Webb in Washington says.
Until now comments the Troops Out movement in America has received support only on the political fringes, but that has changed in a dramatic fashion, our correspondent says.
Mr Murtha's comments came just hours after Mr Cheney called opposition Democrats "opportunists" who were peddling "cynical and pernicious falsehoods" to gain political advantage while US soldiers died in Iraq.
"The president and I cannot prevent certain politicians from losing their memory or their backbone - but we're not going to sit by and let them rewrite history," Mr Cheney said.
A claim that the administration had misled Americans before the war was one of the most dishonest and reprehensible charges ever aired in Washington, the vice-president continued.