A second attack at a checkpoint manned by Iraqi soldiers and another of the U.S-backed groups killed 10 people, an Iraqi army officer said.
The attacks - about 10 miles apart - highlighted the dangers for the U.S.-backed groups, which often include former insurgents who have turned against al Qaeda in Iraq. The groups are credited with helping stem Iraq's violence along with the influx of U.S. troops.
Both bombings were in Diyala, the province just north of Baghdad that remains one of the country's most violent regions despite dramatic security gains in the capital and elsewhere.
In the first attack, in the city of Muqdadiyah, 10 of those killed were members of the local anti-al Qaeda group who have partnered with U.S. and Iraqi forces to rid their neighborhood of militants, said Brig. Gen. Mohammed al-Tamimi, the city police chief, who said the bombing claimed 15 lives and wounded 20. The U.S. military said 12 people died and 17 were wounded.
Ibrahim Bajalan, the head of Diyala provincial council, said the bomber was a former member of Saddam Hussein's Baath Party whose two sons joined al Qaeda and were killed by Iraqi security forces.
"She wanted to avenge the killing of her two sons," he told The Associated Press. He said 15 people died and 35 were wounded when she detonated a belt of explosives.
The U.S. statement there was no confirmation that any of the dead or wounded were part of the anti-al Qaeda group. About half the wounded were taken to a nearby base for treatment, said Maj. Peggy Kageilery, a U.S. military spokeswoman for northern Iraq.
Jassim Jerad, a former Iraqi soldier who was injured in the bombing, said he saw a woman approaching the offices, then felt the explosion.
"I fell down, but stood up quickly to save my son, who was screaming," he said from his hospital bed, while his 6-year-old son wept nearby.
Later Friday, a suicide car bombing at a checkpoint near Mansouriayat al-Jabal killed seven Iraqi soldiers and three members of a local anti-al Qaeda group, according to Iraqi army Capt. Saad al-Zuhairi, who was about 150 yards away. Al-Zuhairi said the driver detonated his explosives when the guards asked to search the car.
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, but has increased in the north, where al Qaeda militants and other extremists are believed to have fled a U.S.-led security crackdown that began in mid-February in Baghdad.
As the influx of U.S. troops gained momentum earlier this year, American officials have courted both Sunni and Shiite tribal leaders around the country, hoping they will help lead local drives against al Qaeda and other militants. 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, and members have come under increasing attack from militants trying to offset recent security gains.
Since the groups began forming in Diyala in July, many of their members have faced deadly militant strikes. In Baqouba, at least 13 have died in suicide attacks, roadside bombings shootings, according to records compiled from local police.