U.S. and Iraqi forces launched a major attack against insurgent holdouts in the Iraqi city of Fallujah Saturday, trying to smother all resistance in the former rebel stronghold.

Witnesses say troops fired a barrage of mortar shells in Fallujah's Jolan district, in the city's northwestern quarter, while tanks and artillery fire supported troops moving house to house in southern parts of the city.

U.S. military officials say coalition forces now control of most of Fallujah. They estimate 600 insurgents were killed in five days of urban fighting.

The Iraqi Red Crescent sent a four-vehicle convoy of food, medicine and other supplies to Fallujah Saturday, hoping to enter the city to assist civilians trapped by the fighting. However, military commanders say it may be too dangerous to allow the convoy to enter the battle zone.