BAGHDAD - Iraq's prime minister dropped his protection of the feared Shiite militia of an anti-American cleric after U.S. intelligence convinced him the group was infiltrated by death squads whose actions were isolating him in the Arab world and among moderates at home, two officials said yesterday.

In a bid to fend off an all-out American offensive, the cleric, Muqtada al-Sadr, on Friday ordered the 30 lawmakers and six cabinet ministers under his control to end their nearly two-month boycott. They were back at their jobs yesterday.

Sadr had already ordered his militia fighters not to display their weapons. They have not, however, ceded control of the formerly mixed neighborhoods they have captured, killing Sunnis or forcing them to abandon their homes and businesses.

Prime Minister Nouri al-Maliki's turnaround on the Mahdi Army was puzzling because as late as Oct. 31, he had intervened to end a U.S. blockade of Sadr City, the northeast Shiite enclave in Baghdad that is headquarters to the militia. It is held responsible for much of the sectarian bloodshed that has turned the capital into a battle zone over the last year.

Shiite militias began taking revenge after more than two years of incessant bomb and shooting attacks by Sunni insurgents.

Sometime between then and Nov. 30, when the prime minister met with President Bush, Maliki was convinced of the truth of American intelligence reports and other evidence about the militia, the two government officials said.

"Maliki realized he couldn't keep defending the Mahdi Army because of the information and evidence that the armed group was taking part in the killings, displacing people, and violating the state's sovereignty," said one official. Both he and a second government official who confirmed the account refused to be identified by name because the information was confidential.

"The Americans don't act on rumors but on accurate intelligence. There are many intelligence agencies acting on the ground, and they know what's going on," said the second official, confirming the Americans had given Maliki overwhelming evidence about the Mahdi Army's deep involvement in the sectarian slaughter.

Earlier this month, Bush and Maliki separately announced a security drive to clamp off the sectarian violence that has riven the capital and surrounding regions.

Bush announced an additional 21,500 American soldiers would be sent to accomplish the task, and Maliki has promised a similar number of forces, who will take the lead in the overall operation.

Iraq's Special Forces Command division has already teamed with the Americans since late last year for a series of pinpoint attacks in which at least five top Mahdi Army figures have been killed or captured.

The neighborhood-by-neighborhood sweep, expected to begin in earnest by early February, will target Sunni insurgents, al-Qaeda in Iraq, and its allied militant bands equally with Shiite militias, both the Mahdi Army and the Badr Brigade.

The latter is the Iranian-trained military wing of Iraq's most powerful Shiite political group, the Supreme Council for the Islamic Revolution in Iraq.

The first government official said Maliki's message was blunt.

"He told the sheik [Sadr] that the activities of both the Sadrist politicians and the militia have inflamed hatred among neighboring Sunni Arab states that have been complaining bitterly to the Americans," the official said.

Sunni Muslims are the majority sect in key Arab countries, such as Saudi Arabia, Jordan and Egypt, all of which have shunned Maliki. Shiites, long oppressed by Iraqi's Sunni minority, vaulted to power with the ouster of Saddam Hussein.

Meanwhile, new details emerged about clashes Saturday in the Shiite holy city of Karbala that left five Americans dead, according to the New York Times.

Lt. Col. Scott R. Bleichwehl, a U.S. military spokesman, said the gunmen who stormed the provincial governor's office during a meeting between American and local officials were wearing what appeared to be U.S. military uniforms in an effort to impersonate U.S. soldiers.

It is not uncommon for gunmen to impersonate Iraqi security forces, but this seemed to be the first time that attackers have tried to disguise themselves as Americans, the Times said.

In other fronts

The U.S. military yesterday reported six more American troops killed in fighting the day before, raising the toll to 25 in the deadliest day for U.S. forces in Iraq in two years.

Four U.S. soldiers and a Marine were killed Saturday in combat in Anbar province, the Sunni insurgent stronghold west of Baghdad, the military said. A roadside bomb also struck a security patrol northeast of Baghdad, killing one soldier.

Saturday's carnage also included 12 soldiers killed in a Blackhawk helicopter crash northeast of Baghdad, five killed in a militant attack in the holy Shiite city of Karbala, and two others slain elsewhere in roadside bombings.

In violence reported by Iraqi police yesterday:

A bomb left in a bag struck a small bus carrying people to work in a predominantly Shiite area in Baghdad, killing seven passengers and wounding 15.

A parked car bomb exploded outside a restaurant in eastern Baghdad, killing one person and wounding five.

A suicide car bomber targeting an Iraqi army patrol killed one woman and wounded five other people in the northern city of Mosul.

Morgue officials reported that 29 people were found dead in Baghdad, most of them showing signs of torture.