Gunmen killed three guards from a U.S.-allied Sunni group Thursday in drive-by shootings in northern Baghdad, an official said.

The attackers opened fire as they sped by two different awakening council checkpoints in the Azamiyah neighborhood, according to a leading member of the group, who spoke on condition of anonymity because of security concerns.

Azamiyah has seen a sharp decline in violence after a local Sunni decision to join forces with the United States against Al Qaeda in Iraq. The area also has been surrounded by concrete walls in a bid to stem attacks.

Members of the so-called awakening councils have frequently been targeted by militants seeking to derail security gains or in reprisal killings.

The Sunni revolt has been credited by the U.S. military as a key factor in driving down violence to its lowest point in more than four years — along with an American troop buildup and a cease-fire by anti-U.S. cleric Muqtada al-Sadr.

In a grim reminder of the dangers still facing Iraqis, the 18-year-old son of the chief editor of a U.S.-sponsored newspaper was shot to death as an American patrol passed nearby in the northern city of Kirkuk, police said.

Police Brig. Gen. Sarhat Qadir said it was unclear who fired the bullet that killed Arkan Ali Taha, suggesting it might have been a sniper aiming at the Americans.

"Police until now are still investigating and we can't say whether the Americans are to blame or the attackers," Qadir said.

The U.S. military said American troops came under small-arms fire from a purple sedan while they were on a foot patrol in the volatile city.

"The soldiers returned fire in self defense, killing a passenger in the car. The driver of the vehicle was taken into custody," the military said, adding that one soldier was wounded in the gunbattle.

The young man's father, Ali Taha, blamed the Americans for his son's death.

"My son was in his car when shots fired from an unidentified place targeted the Americans," he said. "It happened that my son was nearby and I blame the Americans for shooting him."

In other violence Thursday, a bomb exploded near the house of Abdul-Rahman Dawood, a leading figure in the Dawa Party, leaving him wounded in the predominantly Shiite Baghdad neighborhood of Zafaraniyah. The Shiite party is led by Prime Minister Nouri al-Maliki.

The U.S. military, meanwhile, said American troops captured 20 suspected militants linked to Al Qaeda in Iraq in raids Wednesday and Thursday in operations to the north and south of Baghdad.