BAGHDAD, Iraq - In the fiercest and most extensive fighting in Iraq since President Bush declared an end to major combat in Iraq in May, U.S. and allied troops battled insurgents in at least five Iraqi cities on Wednesday.

In what was believed to be the day's deadliest single incident, U.S. Marines battling for control of Fallujah reportedly fired rockets that landed near a mosque, killing approximately 40 people, according to witnesses.

An Associated Press reporter in the city saw cars ferrying the bodies from the Abdul-Aziz al-Samarrai mosque. A wall surrounding the mosque was demolished, though the mosque itself was not damaged, the reporter, Abdul-Qader Saadi, said.

Witnesses said that three missiles had landed near the building as worshippers were gathering for afternoon prayers. There was no immediate confirmation from the U.S. military.

If confirmed, the figure would push the number of Iraqis killed Wednesday well past 100. Only two U.S. soldiers were reported killed in the latest round of combat.

But a commander confirmed Wednesday that 12 Marines were killed a day earlier in the western city of Ramadi, and at least 18 U.S. troops have been reported killed in the fighting in Fallujah, part of an intensified and spreading uprising involving both Sunni and Shiites stretching from Kirkuk in the north to near Basra in the south.

Fallujah is scene of heaviest fighting
The heaviest fighting Wednesday appeared to be occurring in Fallujah, where U.S. Marines were fighting their way into the city block by block, firing on insurgents and pounding houses with tank shells and rockets in a drive to pacify one of Iraq’s most dangerous cities.

The Americans also called out a weapon rarely used against the Iraqi guerrillas: the AC-130 gunship, a warplane that circles over a target, laying down a devastating barrage of heavy machine gun fire. At least 60 Iraqis were killed and more than 120 wounded in overnight fighting in Fallujah, hospital officials said.