US soldiers watch as a plume of smoke rises from an air-strike they ordered to destroy a desert cave complex used by insurgents in Diyala Province. The death toll of US soldiers in the five-year Iraq conflict has hit 4,000 in what the US military said Monday was a "tragic" loss of lives after four troops were killed in a Baghdad bombing. (Xinhua/AFP Photo)

The US military said Monday that a roadside bomb killed four US servicemen Sunday night, pushing the death toll to 4,000 shortly after the fifth anniversary of the Iraq war.

The military said in a statement that the four died when their vehicle came under a roadside bombing attack in southern Baghdad. One additional soldier was injured.

The new record came amid heated debate in the US presidential campaign about weather the troops should be pulled out soon.