Baghdad ? Dozens of suspected al-Qaida militants showered a Shiite village with mortar rounds early Saturday, then stormed the streets, killing at least 13 Iraqis, torching homes and forcing hundreds of families to flee, police said.

Some villagers fought back, leaving three gunmen dead in the heart of one of Iraq’s most violent regions.

Even with nationwide violence ebbing to the lowest levels since January 2006, American commanders have warned that security is precarious in northern Iraqi regions such as Diyala – where Saturday’s attack took place – as al-Qaida and other militants have moved there to avoid coalition operations.

The militant attack on Dwelah, about 45 miles north of Baghdad in Diyala, began about 6:30 a.m. with the mortar rounds, then 50 to 60 suspected al-Qaida fighters streamed in and opened fire, a police officer said.

Among the 13 dead were three children and two women, the officer said, speaking on condition of anonymity because he was not authorized to release information about the raid. Villagers trying to fight back killed three gunmen, but the militants torched more than two dozen homes and about 500 families took shelter in neighboring towns, police said.

Elsewhere in Diyala, Iraqi officials said U.S. and Iraqi troops, police and members of a local tribe freed four villages from al-Qaida control, killing 10 militants and arresting 15 in a two-day operation that ended Saturday.

Among the weapons and ammunition seized were 100 barrels of TNT, according the provincial army and police headquarters. The U.S. military said it could not immediately confirm the report.

As the influx of U.S. troops gained momentum earlier this year, American officials have courted Sunni and Shiite tribal leaders in Diyala and elsewhere, hoping they will help lead local drives against al-Qaida. A similar effort saw some success in Iraq’s westernmost province, Anbar, where Sunni tribes rose against the organization’s brutality and austere version of Islam.

The groups now include some 60,000 Iraqis nationwide, most of them Sunni Arabs, according to the U.S. military. At least six members of the local groups were killed on Friday and Saturday outside Baghdad and five were abducted, police and group members said.

At least 35 Iraqis were killed or found dead across the country, according to an Associated Press count Saturday. Also Saturday, a roadside bomb struck a U.S. combat patrol in Baghdad, killing one American soldier and wounding three, the military said in a statement.

U.S. commanders have welcomed the relative lull in violence, but warn that Sunni and Shiite extremists still pose a serious threat. The U.S. administration has pushed the Shiite-led government to capitalize on the security gains and make tangible progress toward national reconciliation.

That effort has foundered, and on Saturday lawmakers from parliament’s largest Sunni Arab bloc walked out of a session to protest what they called the house arrest of their leader, Adnan al-Dulaimi, following the discovery of a car bomb near his compound.

U.S. and Iraqi officials said the keys to the explosives-laden vehicle were found on one of his bodyguards. Al-Dulaimi’s son and about 30 other people also were arrested Friday.

Lawmakers said al-Dulaimi, a harsh critic of Shiite Prime Minister Nouri al-Maliki, told them Saturday that security forces prevented him from leaving his Baghdad home to come to parliament, which is located in the U.S.-protected Green Zone. Also stopped from leaving was his daughter, legislator Asmaa al-Dulaimi.

Chief government spokesman Ali al-Dabbagh denied in an interview with state television Saturday that al-Dulaimi was under house arrest, but added that any proceedings against him would be carried out under the law.

“Everyone is subject to the law whether he is a lawmaker or not and the government is adamant to be objective and neutral in dealing with this issue,” he said.