U.S. warplanes and tanks bombed suspected insurgent positions in the volatile city of Fallujah (search) for more than two hours on Wednesday, killing at least four people, hospital officials and residents said.

Witnesses said U.S. warplanes strafed targets at least 15 times on the city's eastern outskirts, and strong explosions could be heard. Militants fired anti-aircraft guns in response as U.S. aircraft approached.

At least four people were killed and four wounded in the bombings, said Adel Khamis, a doctor at Fallujah General Hospital.

A Marine spokesman, Lt. Col. Thomas V. Johnson, said that several insurgent "firing positions ... have been struck this morning with tank-fire and yes, aircraft were also used against the targets."

It was the second day in a row that U.S. forces struck at the city, located 40 miles west of Baghdad.

Sunni insurgents (search) based in Fallujah are believed responsible for months of kidnappings, bombings and shooting attacks against coalition troops, Iraqi forces and civilians across Iraq.

U.S. forces have routinely bombed targets here it describes as insurgent safehouses or strongholds.

After Tuesday's airstrikes, the military issued a statement saying they had "destroyed a position occupied by numerous foreign terrorists, as well as a weapons cache."

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 to hit targets here.