Six U.S. soldiers were reported Wednesday to have been killed in Iraq, while the country's interim prime minister threatened a major offensive against the city of Fallujah unless its residents hand over Abu Musab Zarqawi, the Jordanian guerrilla leader thought to be hiding there.

Two of the U.S. soldiers were killed Wednesday when a suicide bomber drove his car into a U.S. convoy in the northern city of Mosul, a tactic that has grown more frequent among insurgents in recent weeks. Another soldier died when a roadside bomb was detonated in west Baghdad, the military said.

The three other U.S. deaths occurred Tuesday night when a roadside bomb exploded near a convoy in Sadr City.

At a meeting of Iraq's National Council, the interim prime minister, Ayad Allawi, said that if the people of Fallujah "do not turn in Zarqawi and his group, we will carry out operations in Fallujah." He added: "We will not be lenient."

Allawi's threat reflected continuing efforts by Iraqi and U.S. officials to press residents of the city of about 300,000 to allow the interim government to reestablish control there. A delegation from Fallujah has been meeting with officials in Baghdad to negotiate a deal that would allow the Iraqi National Guard to peacefully enter the city, which has been controlled by insurgents for six months and has become a refuge for foreign guerrillas such as Zarqawi, the best known of the Sunni Muslim insurgents blamed for scores of attacks in Iraq.

The government has said repeatedly that foreign insurgents must be removed. The demand that Zarqawi and his followers specifically be handed over has been rejected by the Fallujah delegation, which instead agreed to simply eject all foreign fighters.

It was unclear Wednesday whether Allawi was holding tight to that demand or simply trying to make the foreigners even more unwelcome in Fallujah than many residents say they already are. The foreigners are often blamed for U.S. airstrikes on homes in the city and have been condemned by local insurgents for carrying out beheadings and other atrocities.

Residents have grown especially fearful of an attack since Oct. 1, when an armored U.S. brigade took control of Samarra, another city in the Sunni Triangle north and west of Baghdad that had been controlled by insurgents. Iraqi and American officials say the assault on Samarra was part of a broader campaign to bring all insurgent-held areas under Baghdad's control before elections planned for January.

"I would like to reassert once more that the option of using force is a last resort," Allawi said. "We shall remain prepared to deal positively with any initiative to disarm and enter the political process."

The ambush that killed three American soldiers in Sadr City, the vast Shiite Muslim slum in eastern Baghdad, underscored the challenges facing what U.S. officials describe as a peace initiative there rather than a formal cease-fire with an unevenly disciplined, homegrown force.

Shiite militiamen in the city have been turning in weapons and explosives as part of a plan to pacify the capital's most stubborn insurgent trouble spot. Under terms of the deal, members of the militia loyal to Moqtada Sadr, a junior Shiite cleric, are also obliged to dig up mines, artillery shells and other crude munitions known as improvised explosive devices, or IEDs, planted along roads and typically detonated by remote control as U.S. patrols pass.

On Monday, the first of five days set aside for the weapons turnover, militiamen knelt on the fetid streets of Sadr City, excavating and removing munitions.

"It just illustrates that we know there are a lot of IEDs and bomb-making stuff out there," said Lt. Col. James Hutton of the Army's 1st Cavalry Division. "They have got to cut this stuff out and bring it in."

Hutton said the pace of the weapons handover picked up after a slow start Monday, "but there are way too many weapons on the street. Unless that stuff is turned in in huge numbers -- I mean massive numbers -- we're going to be skeptical about the intent of them to live up to this.

"The proof of intent . . . is what this is about more than anything," he said. "We're going to have to see it."

Iraqi police stand guard in the northern city of Mosul after a suicide bomber drove his car into a U.S. convoy, killing two soldiers. Another soldier died when a roadside bomb was detonated in west Baghdad, the military said.Iraqi National Guardsmen in the Sadr City area of Baghdad check land mines that were turned in at a police station, part of a weapons-for-cash program.