American forces pushed deeper into the southern reaches of Fallujah, cornering militants backed into smaller pockets of the city. Hundreds of men trying to flee were turned back by U.S. troops.
On Friday, Army and Marine units moved to tighten their security cordon around the besieged city, backed by FA-18s and AC-130 gunships.
Some three to four dozen militants tried to break out towards the south and east late Thursday but were repelled by U.S. troops, the military said.
U.S. forces were also positioned to the west near key bridges, blocking rebels from crossing the Euphrates River with patrol boats.
The four-day Fallujah offensive has killed some 600 insurgents, 18 U.S. troops and five Iraqi soldiers, the U.S. military said. An additional 178 Americans and 34 Iraqi soldiers have been injured, the military said.
Troops have cut off all roads and bridges leading out of the city and have turned back hundreds of men who have tried to flee the city during the assault. Only women, children and the elderly are being allowed to leave.
The military says keeping men aged 15 to 55 from leaving is key to the mission's success.
In other highlights:
Overnight in Fallujah, U.S. troops launched another mass offensive south of the main east-west highway that bisects Fallujah, a Sunni Muslim insurgent stronghold 40 miles west of Baghdad.
An Iraqi journalist in the city reported seeing burned U.S. vehicles and bodies in the street, with more buried under the wreckage. He said two men trying to move a corpse were shot down by a sniper.
Two of the three small clinics in the city have been bombed, and in one case, medical staff and patients were killed, he said. A U.S. tank was positioned beside the third clinic, and residents were afraid to go there, he said.
"People are afraid of even looking out the window because of snipers," he said, asking that he not be named for his own safety. "The Americans are shooting anything that moves."
Many, if not most, of Fallujah's 200,000 to 300,000 residents fled the city before the assault. It is impossible to determine how many civilians who were not actively fighting the Americans or assisting the insurgents may have been killed.
Commanders said they believe 1,200 to 3,000 fighters were in Fallujah before the offensive.
Most of the insurgents still fighting in Fallujah are believed to have fallen back to southern districts ahead of the advancing U.S. and Iraqi forces, although fierce clashes were reported in the west of the city around the public market.