BAGHDAD (AP) — An al-Qaida front organization claimed responsibility Saturday for a suicide bombing that killed more than 20 people — including three Marines — as the U.S. military stepped up pressure on extremists in northern Iraq.

The Islamic State of Iraq posted the claim on a militant Web site, saying the bomber blew himself up among a gathering of the "heads of apostasy" — a reference to U.S.-backed Sunni tribal leaders who were attending a meeting Thursday in Karmah, 20 miles west of Baghdad.

"They sold their souls to the American devil for a cheap price," the statement said. "Therefore, the soldiers of the Islamic State of Iraq have launched an open war against them."

The dead included the commander of Marines in the area, Lt. Col. Max A. Galeai of Pago Pago, American Samoa, as well as the mayor of Karmah, several key tribal figures and two interpreters, U.S. and Iraqi officials said.

It could not be determined if the statement was actually issued by the Islamic State, which is an al-Qaida-controlled coalition of Sunni extremist groups.

However, U.S. officials suspected al-Qaida was behind the attack as part of a campaign of revenge against Sunni community leaders who turned against the terror movement and cooperated with U.S. and Iraqi authorities.

The Sunni revolt against al-Qaida, which gained steam two years ago, cost the terror movement much of its base in vast Anbar province, the heartland of Iraqi's Sunni Arab community and former center-stage of the Sunni insurgency against U.S.-led coalition forces.

The Karmah attack happened two days before U.S. officials planned to formally hand over security responsibility for Anbar to the Iraqis — a sign of the security transformation in the largest of Iraq's 18 provinces.

U.S. authorities postponed the ceremony Friday because of forecast sandstorms, which struck Anbar and areas of western Baghdad as predicted Saturday.

Also Saturday, Azerbaijan's Defense Ministry announced that a 20-year-old serviceman from the former Soviet republic had been killed near the Anbar city of Haditha, where that country's troops guard a hydroelectric dam on the Euphrates River.

A ministry statement said the service member died Friday but did not give a cause of death. Azerbaijan had about 150 troops in Iraq and the soldier was the first to have died in Iraq.

Elsewhere, the U.S. command said American and Iraqi soldiers stepped up pressure this weekend on al-Qaida and other Sunni militants across northern Iraq.

Two militants were killed in a gunfight in Sharqat, about 170 miles north of Baghdad, the military said in a statement. One of the dead was identified as a wanted member of a network that carries out bombings, the military said.

Eight others were apprehended in the raids.

A third suspected militant was killed Saturday in nearby Kirkuk during a raid on a cell believed to have carried out kidnappings.

A U.S. military statement said troops opened fire after an armed man refused to surrender and began "to move quickly with his weapon into a confrontational position."

Three others were detained Friday in the northern city of Mosul, including an alleged leader of an "illegal terrorist court" that meted out punishment and supervised suicide bombers, the U.S. military said.

A suspect believed to have ties to senior al-Qaida in Iraq figures was picked up Saturday in Bulayj, about 60 miles southwest of Mosul, the U.S. said.

In Samarra, 60 miles north of Baghdad, Iraqi police reported finding an estimated 30 human remains in an area west of the city near Lake Tharthar where al-Qaida had been active.

Police Lt. Muthana Shakir said the remains included six women and most of the bodies were handcuffed.