FALLUJAH, Iraq -- US forces yesterday pummeled what commanders said were the last insurgent strongholds here, two narrow patches of territory on the southern edge of Fallujah, fortified by bunker and tunnel complexes.
The drive into the two neighborhoods, led by Army tanks and Bradley fighting vehicles, and including Marines, brought the heaviest fighting of the offensive. Insurgents holed up in metal-roofed trenches, and groups of 20 fighters repeatedly attacked armored columns with rocket-propelled grenades.
Although Iraq's national security adviser, Qassem Dawoud, proclaimed the Fallujah mission ''accomplished" yesterday, the remaining insurgents continued to put up a fight, and the US military said it may take days to completely subdue them. The operation in Fallujah, which began Monday, has killed at least 24 US troops, five Iraqi soldiers, and an estimated 1,000 insurgents. There have been no reliable reports on civilian casualties.
The actions of one US unit yesterday reflected the challenges that remain. Lieutenant Colonel Peter Newell of the Army's First Infantry Division's Task Force 2-2, said early in the day that he was confident the remaining guerrillas would be defeated within hours.
''We have these guys in a box that's 1,000 meters long and 500 meters wide," he told a Globe reporter traveling with the Army. ''In a couple of hours, we're going to drop every bit of close air support and every bit of artillery and an entire armored task force."
By evening, however, the attack had proved more complicated, with troops penetrating only partly into the neighborhood after logistical problems. In one case, a tank got stuck after falling through an insurgent tunnel. Still, Newell said, ''There is no organized resistance left in this sector."
Insurgents in the northern city of Mosul, meanwhile, continued to roam the streets, provoking fears that the Falllujah assault would merely disperse the insurgency across the country while, in the city, the destruction fanned public dissatisfaction with the US-backed government. The US command withdrew a battalion of the 25th Infantry Division in Fallujah and returned it to Mosul after insurgents attacked police stations, bridges, and government buildings Thursday.
Elsewhere, fighting was reported in Qaim on the Syrian border and in Hit and Ramadi, closer to Baghdad. At least four Iraqis were killed in a US airstrike on rebels and clashes yesterday in the Abu Ghraib suburb of western Baghdad, police said.
The Iraqi government said Baghdad's international airport, initially closed Monday night for 48 hours, would close indefinitely because of security concerns.
Since Thursday night, when the First Cavalry Division pushed into Fallujah's Shuhada district and First Infantry Division troops attacked a neighborhood in the city's southeastern corner, insurgents have killed a US tank crewman and a machine gunner and wounded nine soldiers.
In yesterday's operation, Newell's troops found a bunker system more than 500 yards long that he said seemed to have been a training facility for insurgents. After insurgents attacked a tank platoon with RPGs, Newell unleashed an intense barrage on a narrow strip of territory where he said the last fighters on the southeastern half of the city were holed up.
A warplane dropped a 500-pound bomb on a house where a sniper was seen, followed by artillery rounds and tanks that pounded the rubble at close range.
The rebels are running out of room to maneuver and are suffering from shortages of food and water, eating only fruit taken from abandoned shops, one fighter said. ''We did not eat anything for a whole day now," Abu Kamil said.
US officials said about 14 suspected foreign fighters have been captured; Dawoud confirmed yesterday that Abu Musab al-Zarqawi, the Jordanian whom US officials have blamed for much of the violence in Iraq, and Fallujah leader Abdullah al-Janabi had escaped.
Saif al-Deen al-Baghdadi, an official of the insurgents' political office in Fallujah, urged militants to fight US forces outside Fallujah. ''I call upon the scores or hundreds of the brothers from the mujahideen . . . to press the American forces outside" Fallujah, Baghdadi said in a telephone interview late Friday with Al-Jazeera television, which also showed a video of Islamist groups, pledging to take the fight to all corners of Iraq.
It is unclear how many of Fallujah's 300,000 residents remain, but more than half are thought to have fled before the ground assault had begun. Five trucks of an Iraqi Red Crescent convoy reached Fallujah yesterday with the first aid since US-led forces invaded.
''Conditions in Fallujah are catastrophic," said Firdoos al-Abadi, a representative of the organization.
An Iraqi correspondent for the Globe contributed to this report; material from wire services also was included.