The number of US soldiers to die in Iraq has reached 4000, the US military said on Monday, just days after the fifth anniversary of a war that President George Bush says the United States is on track to win. 

The US military said in a statement four soldiers were killed late on Sunday when a roadside bomb, the biggest killer of American soldiers in Iraq, exploded near their vehicle in southern Baghdad. One soldier was wounded in the attack. 

What impact the grim milestone will have on a war-weary American public and the US presidential campaign will be hard to assess in the short term, but war critics are likely to seize on it to boost their case for US troops to be withdrawn. 

The US military dismisses such tolls as arbitrary markers. 

"It is artificial in the sense that somehow the 4000th tragic loss somehow will be different from the first," US military spokesman Rear Admiral Greg Smith said last week. 

Anthony Cordesman, a respected Iraq analyst at the Centre for Strategic and International Studies in Washington, said the 4000 death could trigger another wave of polarised debate. 

US Death Toll In Iraq Reaches 4000