U.S. forces launched an airstrike Friday in the troubled Iraqi city of Fallujah (search), witnesses said.

A U.S. plane fired at least one missile into an industrial area of the city, located 40 miles west of Baghdad (search), witnesses said. There were no immediate reports of casualties.

The military could not immediately be reached for comment.

The airstrike was the second on Fallujah on Friday. Earlier, a U.S. warplane fired missiles into the same part of the city.

Insurgents responded to the earlier attack by firing mortars toward a nearby U.S. base as calls of "God is Great" and Quranic verses, used to boost the morale of the fighters, blared from the loudspeakers of mosques.

U.S. forces have routinely bombed targets in the city it says are insurgent safehouses or strongholds.

Many of the Sunni insurgents believed responsible for the spate of kidnappings, bombings and shooting attacks at coalition troops, Iraqi forces and civilians, are based in the city.

Since the U.S. Marines pulled back from Fallujah after besieging the city for three weeks in April, the military has been limited to using long distance strikes against targets there.