BAGHDAD, Iraq — U.S. Marines took part in a fierce overnight firefight in Fallujah, the city where a tenuous cease-fire was in place and near where an American helicopter crashed in flames on Tuesday.

Marines defended their position in a school at the northern edge of the city when they came under mortar fire. The U.S. forces responded with rifle and machine-gun fire.

Officials told Fox News that some Marines were wounded in the engagement but no further information was available.

Near Fallujah, witnesses said insurgents fired a rocket to bring down a U.S. military H-53 Sikorsky helicopter. U.S. troops trying to get to the wreckage were forced back after coming under heavy fire from gunmen. The two sides were in a standoff, each some distance from the downed copter.

The wreckage was burning in a field 12 miles east of Fallujah near the village of Zawbaa. Television pictures showed the main body of the craft charred, little but tangled pieces of metal. No bodies could be seen.

The site was between Fallujah and the western Baghdad suburb of Abu Ghraib, where an Apache was shot down by gunmen Sunday, killing its two crew members.