Mohammed al-Zoubai, a resident, said on Monday that the attackers raided Saidan district of Zouba, 20km from Baghdad, overnight and took six residents from their homes, lined them up in a field and shot them dead.
The killers then stormed the home of Attala Ouda al-Shuker, a leader in the Sahwa (Awakening) movement of Sunni tribesmen who joined US forces in 2006, and shot dead three of his sons and four other relatives, al-Zoubai said.
"They killed three of his sons and four cousins," he said, adding that all those killed were members of the Zouba tribe.
The attackers then dumped the bodies at the local cemetery, he added.
"It was an al-Qaeda group and they were wearing Iraqi army uniforms," Zoubai said.
Major-General Qassim Atta, a spokesman for the army's Baghdad operation, confirmed the toll, but gave a different account.
Iraqi police and hospital sources said another deadly attack occurred in northern Kirkuk, where a car bomb exploded in a crowded market place, killing at least six people and wounding 10 others.
"Many cars were set ablaze and many shops heavily damaged due to the powerful explosion," said Major-General Torhan Abdul-Rahman, deputy police chief for the city.
The death toll is expected to rise, police said.
In a third attack, a bomb planted under a car parked near an Iraqi army checkpoint exploded, killing two soldiers and wounding six civilians in Baghdad's Mansour district, police said.
And a roadside bomb wounded three children on Sunday in a small town near Mosul, 390km north of Baghdad, according to police.