BAGHDAD, Iraq — Dozens of Iraqi police officers were missing and feared dead Friday following an ambush of a motor vehicle convoy as incessant violence between the country's Shiite Muslim majority and Sunni Arab minority marred the Muslim day of worship.

The Thursday night ambush, laden with sectarian overtones, was recounted in confusing and contradictory official accounts that have come to characterize much of the inter-communal violence in Iraq.

It occurred near a U.S. base north of the capital as about 80 officers of the Shiite-dominated police force headed back to a police academy in the southern city of Najaf after picking up new vehicles from a training center in Taji, a stronghold of the Sunni-led insurgency.

Iraqis rarely travel the country's perilous roads at night, fearing bandits and insurgents. Maj. Gen. Abbas Karim, a police chief in Najaf, told reporters the convoy departed after U.S. officials refused to let the Iraqis spend the night at the base.

Lt. Col. Barry Johnson, an American spokesman, said the military had "no indication that there ever was any request to stay at a U.S. base."

The clash erupted between Iraqi police officers and suspected Sunni insurgents shortly after the convoy of 10 or so vehicles left the base.

According to a source in the Taji police force, the convoy, which included members of the feared Interior Ministry Special Forces, started shooting randomly when it reached the riverbank, wounding at least 10 locals.

Residents feared the convoy was one of the Shiite death squads with ties to the security apparatus that have been terrorizing Sunni areas, said the source, who asked not to be named.

The Taji police source said at least 20 officers were killed in the ambush, while Karim said the toll was at least 30 dead. The U.S. military said it could confirm only seven dead and five wounded.

So far only about 2 dozen of the 80 officers have been found alive, said Karim.

Johnson said American troops came to the aid of the police officers after the incident, detaining five gunmen, one of whom was wounded.

Shiite clergy, some of whom angrily denounced the ambush, warned Friday of a potential escalation of violence caused by such attacks. Iraqi and U.S. officials worry a political stalemate over the formation of a government, four months after Dec. 15 elections, harms the country's dire security situation.

Religious leaders also criticized the motives of their political counterparts.

"While the government and political parties are deeply involved in their rivalries and arguments, innocent Iraqis keep suffering daily bloodshed and terror," Sheik Mahmoud Issawi, a Sunni cleric leading prayers at Baghdad's Abdul Qadir Gilani mosque, told worshipers.

"Iraqis are the only victims of the current situation."

In the southern city of Basra, meanwhile, 11 employees of a company making concrete blast barriers used at military checkpoints were shot to death in a square Friday morning. The men had been seized by gunmen as they left work Thursday.

Two bombs exploded outside Sunni mosques in Baqouba, a religiously mixed provincial capital about 35 miles northeast of the capital, killing at least four worshippers and injuring eight as they departed the prayer gathering. The attacks against Sunni houses of worship raised the possibility that Shiites might be launching religiously motivated attacks in retaliation for an onslaught of bombings targeting Shiites house of worship, including triple suicide bombing last Friday at a mosque in Baghdad that killed scores of worshippers.

Sunnis accuse Shiite militias acting under the guise of official security forces with abducting and killing Sunni Arabs. On Thursday, Sunni political and clerical groups alleged that nearly 90 more Sunnis had gone missing or been killed by death squads with ties to the Interior Ministry. Officials Friday reported one body found handcuffed and blindfolded with signs of torture in the southern Baghdad.

Contributing: Louise Roug