A fierce urban battle raged throughout the day in the northwestern district of Jolan, where foreign militants are thought to be concentrated.
Correspondents embedded with U.S. troops said the entire area has been booby-trapped with hidden explosives and landmines. They said the militants have had plenty of time to prepare defenses amid the urban topography -- which is one of the most difficult environments in which to conduct a military offensive.
After 18 hours of fighting, U.S. Marines in Jolan had advanced six city blocks south of a railroad station on the northern fringe of the city. The railroad station had been captured at the start of the assault last night. According to the latest reports, those troops were moving house-to-house, street-by-street toward a mosque in the city center about 1 kilometer away.
U.S. Marines could be seen climbing walls and onto rooftops to clear each building of militant snipers.
Intense hails of gunfire were being directed at U.S. tanks as they attempted to move down the narrow streets of Jolan with close support from foot soldiers and Apache attack helicopters.
One U.S. tank commander, Captain Robert Bodisch, told Reuters that his vehicle was disabled while trying to advance down a narrow street in Jolan. Bodisch said a masked militant in a black uniform emerged from behind a wall and hit his tank with a rocket-propelled grenade.
Another tank commander, Captain Christopher Meyers, said he had seen insurgents darting across alleys in groups of two or three with assault rifles and rocket-propelled grenade launchers.
Reports from other parts of the city have been sketchy. Fierce firefights were heard in both the western and eastern parts of the encircled city this afternoon.
But embedded reporters said their limited view from the urban battlefield makes it difficult to put together a broader picture of what is happening.
Some 15,000 U.S. and Iraqi government troops are involved in the offensive.
Most of Al-Fallujah's 300,000 residents have fled the city in recent months. But there are estimates that as many as 50,000 civilians might still be living there. The Pentagon estimates there are between 1,000 and 6,000 insurgents and foreign fighters in Al-Fallujah.
U.S. Defense Secretary Donald Rumsfeld told reporters in Washington yesterday that the battle is expected to be a major setback for anticoalition forces. But Rumsfeld said Pentagon planners do not expect it to be a final showdown.
"It's pretty clear that the extremists would lose a great deal [if they lost Al-Fallujah]," Rumsfeld said. "And I think they're quite determined to not have that happen. So suggesting anything is final -- I think it's a tough business and I think it's going to take time."
Rumsfeld also would not confirm whether similar ground assaults are being planned the nearby insurgent-held cities of Ramadi and Samarra.
"First of all, these judgments and decisions, the basic decision is being made by the Iraqi government. They then discuss it with the coalition forces. And if we agree, we assist in ways we can assist," Rumsfeld said. "So the answer should come from the Iraqi government to a question like that. Second, even if we were planning to go to the cities you mentioned [Ramadi and Samarra], we wouldn't talk about it."
AP reported that hundreds of armed militants were taking up position in the center of Ramadi -- just to the west of Fallujah -- this afternoon. There were no immediate reports of U.S. troops in the city center.
Meanwhile, a hospital official in Baquba to the northeast of Baghdad said 45 people were killed today when insurgents attacked three nearby police stations. That official said all of the bodies have been brought to the morgue where he works. He said at least 25 of the dead were Iraqi police officers.
There also was a suicide bomb attack today at the entrance gate to a large Iraqi National Guard base near the northern city of Kirkuk, killing at least two construction workers.