FALLUJAH, Iraq - As senior Iraqi officials declared Fallujah "liberated," U.S. forces yesterday continued intense combat operations aimed at securing the last section of the city from an insurgent force fighting with surprising discipline, organization and the trappings of a professional army, commanders said.

In the southernmost section of Fallujah, where a showdown still loomed, U.S. soldiers discovered an underground bunker and steel-enforced tunnels connecting a ring of houses filled with weapons, medical supplies and bunk beds.

The fighters in the area were armed with assault rifles and rocket-propelled grenades and dressed in blue camouflage uniforms with full military battle gear. U.S. soldiers reported finding American Meals Ready to Eat and other equipment the U.S. government donated earlier this year to set up a local security force, which was quickly corrupted and taken over by insurgents.

The interim prime minister, Ayad Allawi, announced "a clear-cut victory over the insurgents and terrorists" in Fallujah but acknowledged that fighters had taken parts of the northern city of Mosul and had attacked sites in several other cities.

Commanders said the fighters in Fallujah exhibited more skill on the battlefield than the insurgents who fleetingly engaged U.S.-led security forces in the first days of the battle to retake the city. U.S. military units reported heavy casualties for the second day in a row; 24 troops have been killed since the battle began.

"When we found those boys in that bunker with their equipment, it became a whole new ballgame," said Pfc. Troy Langley, 19, of Wister, Okla. "The way these guys fight is different than the insurgents."

The situation on the ground served to challenge the declarations of senior Iraqi officials, who, as early as Friday, were announcing that the battle for Fallujah was over in time for Iraqis to celebrate today's end of Ramadan in peace.

"It is with all pleasure that I announce to you that operation New Dawn has been concluded," the minister of state for national security, Qasim Dawood, said at a news conference in Baghdad, as Marine artillery and aerial gunships continued to pummel Fallujah, 35 miles to the west. "Major operations have been brought to a conclusion."

U.S. soldiers and Marines, meanwhile, kept fighting.

"We control 90 percent, but the 10 percent that's left is the most difficult," said Capt. Erik Krivda, a member of Task Force 2-2 tactical operations command.

U.S. and Iraqi security forces have been battling fighters in this insurgent stronghold since ground troops followed a barrage of artillery fire into the city Monday night. Dawood said more than 1,000 insurgents had been killed and 200 captured. A militia group, the Army of Mohammad, reported 73 fighters had been killed.

It was unclear how many insurgents remained in the fight, or even in the city. A U.S. military cordon around Fallujah proved porous, with Iraqi reporters entering the city from the south, and fighters leaving the same way. Others escaped by boat across the Euphrates River to the west, according to witnesses.

The insurgents who remained were very low on food, relying on fruit and canned goods, according to witnesses. But the fighters continued to harass U.S. forces, and the Iraqi troops who were trailing them, by moving through the maze of buildings behind the American advance and even answering American psychological warfare operations.

In areas controlled by U.S. forces, loudspeakers mounted on Humvees urged that "all fighters in Fallujah should surrender, and we guarantee they will not be killed or insulted."

From a loudspeaker on a mosque, the fighters replied: "We ask the American soldiers to surrender and we guarantee that we will kill and torture them."

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