A massive car bomb exploded Monday on the outskirts of Fallujah, killing seven U.S. marines and wounding several others in the deadliest attack on Americans since May.

The attack, 15 kilometres north of Fallujah - a stronghold for Sunni insurgents - destroyed two Humvees, witnesses said. U.S. officials said medical teams in helicopters swept into the dusty, barren site to ferry away the injured, and troops sealed off the surrounding area...

The force of the car bomb outside Fallujah sent the vehicle's engine "a good distance" from the site, a military official said on condition of anonymity.

Four Iraqis were wounded by fire from U.S. troops near the site of the bombing, said Ahmed Bassem of the Fallujah General Hospital.