A mother whose three sons were killed by Americans blew herself up and killed 16 other people yesterday as al-Qaeda began a new campaign against former Sunni insurgents who have joined forces with the American military in Iraq.

The suicide bomber, whose sons had been members of al-Qaeda, killed six women and children and ten former fighters from the 1920s Brigades, a hardline insurgency group that until recently was attacking US and Iraqi government forces.

The men had taken up an American offer to turn on their former allies in al-Qaeda as part of the so-called Sunni Awakening, under which more than 60,000 guerrillas joined forces with the US military.

The bomber, identified by Iraqi police only as Suheila, struck in the town of Muqdadiya, in Diyala province, a hotbed for al-Qaeda groups driven from Baghdad and western Iraq by their former Sunni allies, who had become disillusioned with the extremist group's mass slaughter of civilians. She walked into a building used as offices by the 1920s Brigades and started asking questions before suddenly blowing herself up, witnesses said. Almost 30 people were wounded.

Hours later a second suicide bomber killed another ten people after ramming a car rigged with explosives into a checkpoint manned by Iraqi soldiers and Awakening militiamen.

Yesterday, about 1,000 protesters, including many girls, took to the streets of Sadr City after Friday prayers to denounce an al-Qaeda attack in Diyala province last week in which 12 civilians were killed and a similar number abducted.

An al-Qaeda website said that the extremist group had formed a new unit called al-Siddiq Brigades to fight every “apostate and traitor”, and gave warning that the Awakening councils would be targeted.

General David Petraeus, the commander of US forces in Iraq, said this week: “We see al-Qaeda as a very, very dangerous adversary still able to carry out attacks.”

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