Gunmen raided two Shiite homes in Diyala province, a hotbed of Iraq's Sunni-Arab insurgency, and shot and killed 21 men in front of their relatives, police said Saturday.

The attack by suspected insurgents on Friday night targeted members of the al-Sawed Shiite tribe in the village of Balad Ruz, 45 miles northeast of Baghdad, a police officer said, speaking on condition of anonymity to protect his own security, as officials often do in the increasingly volatile province.

Mourners grieve over the death of their relatives killed in Sadr city attacks, in Najaf, 160 kilometers (100 miles) south of Baghdad, Iraq, Friday, Nov. 24, 2006. Funeral processions were underway on Friday for the more than 200 people who were killed by car bombs and mortars in Baghdad's largest Shiite district, the deadliest attack since the war began. [AP]

He said police could not reach the remote village to collect the bodies and take them to a morgue until Saturday morning. The province, almost equally divided between Sunnis and Shiites, is the site of many sectarian attacks.

Also Saturday, U.S. and Iraqi forces killed 22 insurgents and an Iraqi civilian, and destroyed a factory being used to make roadside bombs, during several raids north of Baghdad. No coalition casualties were reported.

Baghdad remained under a 24-hour curfew Saturday as coalition forces tried to prevent a surge of revenge attacks for the five bombings and two mortar rounds that killed 215 people in the Shiite slum of Sadr City on Thursday.

Such violence was particularly gruesome on Friday, when suspected Shiite militiamen seized six Sunnis as they left prayer services at mosques and burned them alive with kerosene in an attack in the mostly Shia neighborhood of Hurriyah.

Iraqi soldiers at a nearby army post failed to intervene in the assault by suspected members of the Shiite Mahdi Army militia or subsequent attacks that killed at least 19 other Sunnis, including women and children, in the same neighborhood, said police Capt. Jamil Hussein.

In recent months, most of the thousands of dead bodies that have been found dumped across Baghdad and other cities in central Iraq have been of victims who were tortured and then shot to death, according to police.

The suspected militia killers often have used electric drills on their captives' bodies before killing them. The bodies are frequently decapitated. But burning victims alive introduced a new method of brutality that was likely to be reciprocated by the other sect as the Shiites and Sunnis continue killing one another in unprecedented numbers.

Friday's gruesome attack capped a day during which at least 87 people were killed or found dead in sectarian violence across Iraq. In Hurriyah, the rampaging militiamen also burned and blew up four mosques and torched several homes in the district, Hussein said.

The chaos cast a shadow over the Amman, Jordan, summit next week between Shiite Prime Minister Nouri al-Maliki and U.S. President George W. Bush.

Politicians loyal to radical anti-American Shiite cleric Muqtada al-Sadr have threatened to boycott parliament and the Cabinet if al-Maliki goes ahead with the meeting. The political bloc, known as Sadrists, is a mainstay of support for al-Maliki. The Mahdi Army is the organization's armed wing.

For a second day Saturday, funeral processions were held in Sadr City for the victims of Thursday's deadly attack by Sunni insurgents there. An official from al-Sadr's main office in Sadr City visited hospitals treating some of the 257 people who were wounded in the attack, and he gave them small donations of cash in envelopes.

Visiting tents that have been set up in Sadr City for families conducting funerals, the official, Ibrahim al-Jabiri, sharply criticized Iraq's government and its forces for failing to stop such attacks.

During three of the coalition raids that took place north of Baghdad on Saturday morning, soldiers killed 10 insurgents near the city of Taji, which is 12 miles north of Baghdad and home to a major U.S. air base. An Iraqi teenage boy also was killed and a pregnant Iraqi woman was wounded in the crossfire, the military said.

U.S. aircraft were called in to destroy a factory being used to make roadside bombs, and soldiers searching the area also found hidden caches of rocket-propelled grenades, machine guns, anti-aircraft weapons and pipe bombs.

Many U.S. soldiers are killed and wounded in Iraq by powerful roadside bombs used by insurgents.

"Coalition forces strive to mitigate risks to civilians while in pursuit of terrorists. It is always a shame when terrorists hide among civilian women and children, putting them in harm's way," the U.S. military said.

In another area north of Baghdad, coalition forces attacked three vehicles carrying 12 insurgents, including one they were searching for because he allegedly was involved in the manufacture of car bombs, the coalition said. The soldiers opened fire on the cars when they ignored warning shots, and all the militants were killed, the military said.

No soldiers or civilians were wounded during that operation. The coalition declined to give its exact location.