A Sunni insurgent coalition led by Al Qaeda in Iraq claimed responsibility on Tuesday for a homicide bombing that hit a U.S.-promoted reconciliation meeting of Shiite and Sunni tribal sheiks, killing 15 people.

The claim came in a posting on an Islamic militant Web forum, signed by the Islamic State of Iraq, the umbrella group set up by Al Qaeda's branch in the country.

The group said it "has promised the government of apostates painful blows, and here it has fulfilled its promise."

"Yesterday, one of the lions of the martyrdom squad, the Abu Omar al-Kurdi Brigades, plunged with his suicide belt into a gathering for national reconciliation ... and God enabled him to reap most of the chiefs of that fetid council," the statement said.

The attack Monday took place in the city of Baqouba, capital of Diyala province northeast of Baghdad, where the bomber set off his blast in a mosque courtyard where many of the participants in the gathering were located. Among the 15 dead were the city's police chief and the provincial security operations chief. Thirty people were wounded, including two U.S. soldiers and the provincial governor.

The attack represented a major challenge to U.S. efforts to bring together Shiites and Sunnis here in Diyala province, scene of some of the bitterest fighting in Iraq. Over the summer, U.S. troops regained control of Baqouba, which Al Qaeda in Iraq had previously declared the capital of its Islamic state.

In its statement, the group claimed that the attack killed 40 people, including high-ranking officers. It said it would release more details of the attack later.

The statement also repeated the Islamic State of Iraq's claim of responsibility for the Sept. 13 assassination of Abdul-Sattar Abu Risha, the mastermind of the Sunni Arab revolt against Al Qaeda in Anbar province.