Police in Abu Ghraib, just outside Baghdad, found a small truck containing the bodies of 15 men who had been tortured in captivity, said police Lt. Maitham Abdul Razzaq. Two other corpses were found in southwest Baghdad; one appeared to have been hanged, said police Capt. Qassim Hassan.

On Sunday, at least three U.S. soldiers and 31 Iraqis were killed, including seven who died when mortars hit just outside the heavily guarded Green Zone in Baghdad, not far from Iraq's Defense Ministry.

Sunni Arabs say Shiite militias have infiltrated the Interior Ministry ¡ª controlled by the biggest Shiite party ¡ª and used death squads to kill Sunnis following the Feb. 22 bombing of a Shiite shrine in Samarra, north of Baghdad. But the killings have gone both ways.

Police said the bodies of six Shiites were found Sunday in the mainly Sunni district of Azamiyah in Baghdad, their hands and legs bound and their bodies showing signs of torture. Two more bodies were found in a mixed district south of Baghdad.

The chief of the Azamiyah district council, Sheik Hassan Sabri Salman, said relatives also identified the bodies of 14 Sunnis kidnapped last week. The bodies were handcuffed with signs of torture, he said. Police did not confirm the deaths.

The Iraqi Islamic Party, the main Sunni faction in parliament and a likely participant in the next Cabinet, warned of "the repercussions of sectarian cleansing." It urged the new government to stop "the criminal gangs" involved in the killings.

Khalilzad also said Iraq's next government must decommission sectarian militias and integrate them into the national armed forces, warning that the armed groups represent the "infrastructure for civil war."

He issued a strong warning Sunday against militias, calling them "a serious challenge to stability in Iraq to building a successful country based on rule of law."

"There is a need for a decommissioning, demobilization and reintegration plan for these unauthorized military formations," he told a news conference with Iraqi President Jalal Talabani in the northern city of Irbil.

A key question will be control of the Interior Ministry, currently held by the Shiite Supreme Council for the Islamic Revolution in Iraq. The SCIRI ran the feared Badr Brigade militia during Saddam Hussein's rule but insists the group has given up arms, a claim many Sunnis reject.