Dozens of masked fighters launched a coordinated attack on police in Samarra, an official said Friday, entering the city at dusk in 20 machine-gun mounted pickups then splitting up to assault checkpoints and a headquarters building.

A policeman, a woman and an 11-year-old girl were killed in two hours of fighting Thursday, a Samara police official said, and 14 suspected Al Qaeda in Iraq insurgents were arrested, the official said on condition of anonymity because he was not authorized to release the information.

Some 60 masked attackers drove into the city at dusk, then split into small groups and assaulted four police checkpoints and the headquarters, the police official said.

Lt. Col. Michael Donnelly, a U.S. military spokesman in northern Iraq, said he had no details on the report by Samarra police, but that an American patrol got into a firefight with gunmen in the city on Friday.

Two insurgents were killed and another captured, Donnelly said. There were no immediate reports of U.S. casualties.

The U.S. command reported that an American soldier was killed in an explosion Friday in Salahuddin province, which includes Samarra, and four soldiers were wounded. It was unclear whether the explosion was linked to the firefight reported by Donnelly.

In the capital, an American Humvee patrol came under fire from rooftops in the primarily Shiite neighborhood of Shula and called in helicopter support; eight insurgents were killed in the ensuing clash, said U.S. Army spokesman Lt. Col. Scott Bleichwehl.

In Najaf, Nassar al-Rubaie, head of a 30-member bloc in parliament loyal to anti-U.S. Shiite cleric Muqtada al-Sadr, said 21 civilians were killed, a "large number" wounded, and several houses destroyed in the Shula fighting.

He blamed Prime Minister Nouri al-Maliki, saying the Shiite-led government "is weak and can do nothing in the face of the occupation — Shula is now regarded as a front line."

Al-Sadr's main office in Baghdad reported 14 civilians killed and 20 injured, and

an official at Noor Hospital in Shula said bodies of 13 people were brought to the facility along with seven badly wounded people. The official spoke on condition of anonymity because of fears for his safety, and his claim could not be independently confirmed.

Bleichwehl, however, said all those killed were positively identified as enemy fighters, and that there were no civilian casualties.

In southern Iraq, authorities in Muthanna province imposed a province-wide curfew after an attack on al-Sadr's offices in a town near the provincial capital Samawah, about 230 miles southeast of Baghdad.

Two of al-Sadr's offices were demolished after being hit with rocket-propelled grenade fire, police said. The buildings were empty at the time and no casualties were reported, but authorities feared the cleric's followers might seek retribution.

"Because of the fear that reprisals might take place during Friday prayers, a decision was taken to impose the curfew across the province," local politician Ahmed Marzuq said.

Al-Sadr has offices in virtually every major town in southern Iraq, as well as many in northern areas with sizable Shiite communities. Some include free health clinics and most have a prayer area or are linked to a mosque.

Elsewhere, the U.S. command said Friday that Iraqi troops and U.S. Special Forces raided a home in the Hit area and seized an Al Qaeda suspect believed to have shot down an American helicopter in 2004.

The forces detained the suspect and a "second person of interest" in the Wednesday raid, and found an assault rifle as well as identification cards and passports. In addition to the helicopter attack, the primary suspect — whose name was not released — is believed to be involved in roadside bombing and sniper attacks on U.S. and Iraqi forces in the region, 85 miles west of Baghdad, the military said in a statement.

U.S. forces also reported killing seven insurgents and detaining 12 others in operations to disrupt Al Qaeda in central and northern Iraq.

In the biggest raid, troops returned to an area east of Tarmiyah, 30 miles north of Baghdad, where they killed 13 terrorist suspects and captured 12 others a week earlier, based on information from local Iraqis, said spokesman Lt. Col. Christopher Garver.

"With the help of the Iraqi community, we basically crippled this cell," he said.