BAGHDAD, Iraq -- A massive car bomb exploded on the outskirts of Fallujah on Monday killing and wounding several U.S. Marines, a U.S. military official said on condition of anonymity.

The blast sent the engine from the vehicle used in the bombing flying "a good distance" from the site, a military official said.

Wounded troops were already being treated, the official said.

Army Maj. John Wagner, a military spokesman in Baghdad, said he was still waiting for an official account from the U.S. Marines of the troops killed and wounded in the blast. Most of the territory west of Baghdad is under control of the U.S. Marines.

U.S. forces have not patrolled inside Fallujah since April, when U.S. Marines ended a three-week siege. The city has since fallen into the hands of insurgents who have used it as a base to manufacture car bombs and launch attacks on U.S. and Iraqi government forces.

The U.S. military has retaliated by launching several air strikes on insurgent safe houses in the city.