A Shiite militia leader accused of forcibly removing Sunnis from their homes north of Baghdad was captured in a raid, while another operation in the same area left 25 people dead, the U.S. military said Saturday.

The commander was detained Friday after U.S. forces raided Khalis, a Shiite enclave of 150,000 people in the volatile Diyala province some 50 miles north of Baghdad. The man led a group of 20 insurgents that was allegedly responsible for a July attack in which Sunnis were forcibly removed and their homes and farms were destroyed, the military said, adding no one was killed or wounded.

The commander, who was not identified, also was suspected of ambushing a Sunni van driver, shooting him and throwing his body in the Tigris River, the military said.

Another pre-dawn raid Friday in the same town killed at least 25 people after troops met a fierce barrage while hunting suspected arms smuggling links between Iran and Shiite militiamen. The military described those killed in airstrikes as fighters, but village leaders said the victims included children and men protecting their homes.

Also Friday, the U.S. military said it was investigating the deaths of three civilians shot by American sentries near an Iraqi-manned checkpoint. Iraqi officials said the victims were U.S.-allied guards and were mistakenly targeted. And on Saturday, the decapitated bodies of two members of an awakening council in Iskandariyah, south of Baghdad, were found. Both were Sunnis.

While details could not be independently confirmed, the reports reflected rising concerns about possible friendly fire killings and the targeting of those who join vigilante-style groups to fight extremists and fill the vacuum left by Iraq's collapsing national police force.

Such claims could hinder crucial U.S. efforts to draw Sunni and Shiite leaders into alliances against insurgent factions such as Al Qaeda in Iraq.

In Baghdad, meanwhile, a U.S. soldier was killed and three others were wounded Saturday by a roadside bombing while they were taking part in a raid against suspected insurgents in the capital, the U.S. military said in a statement.

Four American soldiers were reported killed in earlier incidents — three Friday in roadside bombings in Baghdad and near Beiji to the north, and one Thursday in a small-arms attack in the capital, the military said.

The airstrike deaths came during a U.S. mission to find the commander of a Shiite militia group linked to members of the Quds Force, an elite branch of the Iranian Revolutionary Guards. Ground forces called for air support as they faced an onslaught by gunmen armed with assault rifles and rocket-propelled grenades in Khalis, a Shiite enclave surrounded by Sunni areas, the military said.

Twenty-five militiamen were killed, but the targeted commander was not found, the military said.

A different account was offered by local leaders and hospital officials. They said U.S. aircraft bombed the neighborhood repeatedly, killing at least seven children and local men who organized watches to guard against extremist attacks.

Iraqis routinely assert that civilians are killed in raids by U.S. forces targeting militants, particularly Shiite militia fighters who usually live among the population and serve as protectors for the local community. But Friday's claim was among the largest in terms of numbers.

The U.S. military reiterated Saturday that the 25 killed were insurgents, not civilians.

"We have confirmed that the 25 criminals who were killed were responsible for the attack on our forces and in fact were members of an extremist group operating in the Baqoubah region," the military said in a statement.

It also said it was investigating the checkpoint shooting dispute near Musayyib, 40 miles south of Baghdad.

The brief announcement did not provide other details. But a local police spokesman said those killed were Shiite members of the North of Hillah Awakening Council, a group of Iraqis who have turned against extremists in the area.

Those killed were three members of the council who were guarding a deserted road leading to their village, the spokesman said, declining to be identified because he was not authorized to release the information.

In other developments Saturday, the military said Iraqi police had detained a fellow officer believed responsible for killing the top district official in Iskandariyah, 30 miles south of Baghdad.

Abbas Hassan Hamza, a political moderate, was killed by a bomb that struck his convoy while he was going to work on Thursday. Four of his bodyguards also were killed and one was wounded. The suspect was accused of telling Shiite militia fighters when to detonate the explosively formed penetrator, or EFP, a weapon that the military says is being supplied by Iran.

Hamza had defected two years ago to Prime Minister Nouri al-Maliki's Dawa Party from the largest Shiite party, now known as the Supreme Islamic Iraqi Council.

In Baghdad, meanwhile, a doctor said Saturday that Poland's ambassador to Iraq was being kept in an artificial coma after suffering severe burns in an apparent assassination attempt earlier in the week. Gen. Edward Pietrzyk was wounded when his convoy was ambushed with roadside bombs while traveling Wednesday through downtown Baghdad. A Polish security guard and two others were killed.

Officials had initially said that Pietrzyk only suffered minor injuries, but a doctor treating him in Poland, where he was brought for treatment, described his condition as serious but stable.