Six U.S. soldiers were killed late Tuesday and early Wednesday by separate roadside bombs detonated near their convoys, the military announced, and Iraq's interim prime minister warned the rebel-held city of Fallujah to hand over foreign terrorists or face a major attack.

Ayad Allawi demanded in a meeting of Iraq's interim National Council that residents of Fallujah, 35 miles west of Baghdad, turn over to the government the Jordanian militant Abu Musab Zarqawi and his followers.

"If Zarqawi and his group are not handed over to us, we are ready for major operations in Fallujah," Allawi told the council, according to Reuters news agency. "I hope they [Fallujah residents] will respond. If they don't, we will have to use force."

He also told the council, "We will not be lenient," the Associated Press reported. Allawi called Fallujah "an honest city," but said it has been "manipulated by a deviant bunch that wants to harm Iraq."

The warning coincided with a claim by a group affiliated with Zarqawi to have beheaded two Iraqi intelligence officers purportedly captured in Baghdad on Sept. 28. A video posted on an Islamic Web site Wednesday showed masked gunmen cutting off the heads of two blindfolded captives, Fadhel Ibrahim and Firas Imeil, who had identified themselves as members of the new Iraqi national intelligence service. The video was released in the name of the Brigades of Abu Bakr Sidiq, a group affiliated with Zarqawi's Monotheism and Jihad organization, the AP reported from Cairo.

Zarqawi's group has claimed responsibility for numerous suicide bombings and the killing of several foreign civilians, including two American contractors and a British engineer who were abducted from their house in Baghdad last month. The three subsequently were beheaded one by one in grisly scenes that were recorded with a video camera. In each case -- as in the latest beheadings of the two Iraqis -- a masked militant then held up the severed head for the camera.

In the latest violence against U.S. forces, a bomb killed a soldier in eastern Baghdad before dawn, a U.S. military statement said. Late Tuesday night, three soldiers were killed when a roadside bomb exploded near their convoy in the Sadr City slum.

In the northern city of Mosul, two U.S. soldiers were killed and five other reported wounded when a suicide bomber blew up his vehicle next to a military convoy. Two of the wounded soldiers returned to duty shortly after the attack, AP reported.

Details on the attacks against U.S. troops were scarce. But the Sadr City attack, in particular, underscored the difficulties facing what U.S. officials describe as a peace initiative rather than a formal cease-fire with a homegrown force of uneven discipline.

Shiite Muslim militiamen in Sadr City have been slowly turning in weapons and explosives as part of a plan to bring peace to what has been the capital's most stubborn insurgent trouble spot.

The militia, known as the Mahdi Army, answers to junior Shiite cleric Moqtada Sadr, whom Iraqi officials have urged to renounce armed insurgency and embrace politics.

Under terms of the peace deal, members of Sadr's militia are obliged not only to turn in arms, but also to dig up the buried mines, artillery shells and other "improvised explosive devices" or IEDs, planted along the roadsides and typically detonated by remote control as U.S. patrols pass.

On Monday, the first day of five days set aside for weapons turnover, militiamen were kneeling on the fetid streets of the slum, digging up and removing buried munitions and booby traps.

"It just illustrates that we know there are a lot of IEDs and bomb-making stuff out there," said Lt. Col. James E. Hutton. "They have got to cut this stuff out and bring it in."

Hutton said the pace of the weapons surrender picked up on its second day, after a slow start Monday. "But there are way too many weapons on the street," Hutton emphasized. "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."

Branigin reported from Washington.