BAGHDAD - The head of a key U.S.-backed Sunni group was killed Monday in a double suicide bombing that claimed at least 11 other lives and highlighted the deadly precision of attacks on Sunni leaders choosing to oppose al-Qaida in Iraq.

The main target -- a former police colonel who led resistance to al-Qaida in Iraq in one of its former Baghdad strongholds -- was first embraced by a bomber posing as a friend. Seconds later, the attacker stepped back and triggered an explosion, a witness said.

A suicide car bomber then struck as rescuers tried to evacuate the wounded. At least 28 people were injured in the twin blasts -- the latest in a spate of attacks against Sunnis who have joined a U.S.-supported movement against extremists that is credited with helping sharply reduce violence.

But the mounting al-Qaida in Iraq backlash has stoked worries of a wider showdown brewing as extremists try to reclaim havens and intimidate the so-called "Awakening Councils" opposing them. In an audiotape released Dec. 29, Osama bin Laden warned that Sunni Arabs who join the groups will "suffer in life and in the afterlife."

Monday's bombing occurred at the entrance of a Sunni Endowment office, a government agency that cares for Sunni mosques and shrines, and near an Awakening Council office in Baghdad's northern Azamiyah district, which had been a stronghold of insurgents and a haven for al-Qaida in Iraq.

The first bomber approached Riyadh al-Samarrai, a former police colonel and head of the local Awakening Council, and claimed to be a friend, said one of al-Samarrai's bodyguards, who was wounded in the attack.

As people rushed to aid the wounded, a suicide car bomb exploded just yards away, said Baghdad's chief military spokesman, Brig. Qassim al-Moussawi.