BAGHDAD: Three more US troops have been killed in Iraq, the military said on Tuesday, as the risks of a stepped up security operation kept the month on course to be one of the bloodiest since the 2003 invasion.

In three separate incidents on Monday a marine, a soldier and an airman were killed, bringing the total number of deaths sine March 2003 to 3,399 and May's toll to 56 with only half the month gone by.

Thousands of troops are still scouring insurgent strongholds south of Baghdad for three more soldiers kidnapped on Saturday in a deadly Al Qaeda ambush near the town of Mahmudiyah.

In Monday's attacks, one airman was killed and three wounded when they were hit by a roadside bomb in southern Baghdad, a statement said. On the same day, in a similar attack in the north of the city, a soldier was killed and four more wounded.

And in Fallujah, a Sunni city west of the capital, a marine was killed by small arms fire.—AFP