BAGHDAD: The number of US soldiers who died in Iraq has reached 4,000, the US military said yesterday, just days after the fifth anniversary of a war that President George W. 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.

The deaths came on a day when the US-protected "Green Zone", the government and diplomatic compound in central Baghdad, was hit by repeated rocket and mortar fire, part of an upsurge in violence in the capital and elsewhere.