U.S. forces released the negotiator representing Fallujah on Monday after detaining him for three days, and both sides in talks to end fighting in the insurgent-held Iraqi city said an agreement was still possible.

The negotiator, Khalid Hamoud Jumaili, said he had denied U.S. accusations during questioning that he represents the insurgents. He described his detention as a setback, but said an agreement was still possible if U.S. forces "are sincere with us."

A car bomb exploded on a bridge in the northern city of Mosul after the vehicle slammed into another car. The attack killed five Iraqi civilians and wounded 15, the U.S. military said.

U.S. aircraft struck Fallujah overnight, targeting what the Marines called terrorist safe houses and weapons caches. The airstrikes followed a quiet day in the city largely emptied of women and children, but it was not clear whether the lull was tied to Jumaili's release and softer rhetoric from the interim prime minister, Ayad Allawi, who last week threatened to attack the city unless residents handed over Abu Musab Zarqawi, a Jordanian militant.

In other cities held by insurgents, official Iraqi rhetoric and calibrated U.S. firepower have alternated in what amounts to a carrot-and-stick approach.

"We are trying our best, using all possibilities, to solve it peacefully," Allawi told Iraq's interim National Council, speaking of Fallujah. "We are still carrying the olive branch."

Jumaili, who heads an insurgent group known as Mohammad's First Army, and other Iraqis continued to deny that Zarqawi resides exclusively in Fallujah. Mohsen Abdul Hamid, president of the Iraqi Islamic Party, called the government's demands "impossible to fulfill. How can the people of Fallujah surrender Zarqawi if he moves here and there in Iraq?"

But Allawi reaffirmed that he believes Zarqawi, whose organization has asserted responsibility for numerous attacks, is in Fallujah. "Zarqawi and [Osama] bin Laden's men are there," he said.

Although their numbers are not known, foreign fighters are believed to represent a significant portion of the insurgents who control Fallujah, a predominantly Sunni Muslim city 35 miles west of Baghdad.

The U.S. military did not initially confirm Jumaili's detention and has yet to explain it. Jumaili said he was seized at a checkpoint outside Fallujah while en route to Baghdad to resume negotiations with representatives of the interim Iraqi government.

"I told them that I am the head of the delegation to negotiate with the government," Jumaili told al-Arabiya television. "When I told them this, it was like I exploded a bomb in their faces. They immediately arrested me."

Jumaili said he was asked questions about his relationship with the insurgents.

He said he later was told that his detention had been "a mistake."

Meanwhile, three U.S. soldiers were wounded Monday afternoon when a roadside bomb exploded in western Baghdad, the U.S. military said in a statement.

The attack in Mosul brought the number of Iraqis killed by car bombs in the past two days to at least 12. Another car bomb exploded in Baghdad late Sunday night, killing seven Iraqi police officers.

U.S. forces reported 30 car bomb incidents in the first 13 days of October. That figure includes car bombs that exploded and others discovered and detonated by U.S. forces.

Fifty-nine car bombs exploded in September, the most in one month since the invasion of Iraq last year. The car bomb attacks accounted for nearly 60 percent of all attacks against U.S.-led forces that month.

Iraqi men sit in the rubble of their house, which was destroyed during fighting in Fallujah, a predominantly Sunni Muslim city west of Baghdad.