The most prominent figure in a U.S.-backed revolt of Sunni sheiks against Al Qaeda in Iraq was killed Thursday by a bomb planted near his home in Anbar province, 10 days after he met with President George W. Bush, Iraqi and U.S. officials said.

Abdul-Sattar Abu Risha and two of his bodyguards were killed by a roadside bomb planted near the tribal leader's home in Ramadi, Anbar's provincial capital, said Col. Tareq Youssef, supervisor of Anbar police.

Abu Risha was leader of the Anbar Salvation Council, also known as the Anbar Awakening — an alliance of clans backing the Iraqi government and U.S. forces. His death deals a sharp blow to American efforts to recruit tribal leaders to fight terror.

No group claimed responsibility for the assassination but suspicion fell on Al Qaeda in Iraq, which U.S. officials say has suffered devastating setbacks in Anbar thanks to Abu Risha and his fellow sheiks. It's unclear how his death would affect U.S. efforts to organize Sunnis against the terror network.

Two Pentagon officials, speaking on condition of anonymity because they were not authorized to speak on the matter, said the assassination would be a huge setback for U.S. efforts in Iraq, because it sends a message to others who are cooperating with coalition forces or thinking about cooperating against Al Qaeda.

During a visit this month to al-Arad Air Base, Bush hailed the courage of Abu Risha and others "who have made a decision to reject violence and murder in return for moderation and peace."

"I'm looking forward to hearing from the tribal leaders who led the fight against the terrorists and are now leading the effort to rebuild their communities," Bush said. "I'm going to reassure them that America does not abandon our friends, and America will not abandon the Iraqi people."

A spokesman for Gen. David Petraeus, the top U.S. commander in Iraq, confirmed the sheik's death in an e-mail from Washington, where Petraeus has been testifying before Congress on the state of conditions in Iraq.

Petraeus pointed to success in Anbar province repeatedly during his appearances on Capitol Hill and in a number of press interviews.

Abu Risha's alliance with the U.S.-backed regime in Baghdad drew threats on his life from Al Qaeda and other militant groups. However, he had recently begun traveling with fewer bodyguards, as the security situation improved in Anbar.

Within two hours of Abu Risha's death, Islamic extremist Web sites posted banners praising the sheik's killing. One called him "one of the biggest pigs of the Crusaders," in an apparent reference to U.S. forces in Iraq. Abu Risha would spend Ramadan "in the pits of hell," another posting said.

But many Ramadi residents reacted to the news of Abu Risha's death with shock and sadness, calling the sheik a "hero" who helped pacify their city.

"We were able to reopen our shops and send our children back to school," said Alaa Abid, 30, who owns an auto parts store in Ramadi. "Now we're afraid that the black days of Al Qaeda will return to our city."

A senior member of Abu Risha's group, Sheik Jubeir Rashid, called the assassination a "criminal act" and blamed Al Qaeda.

"It is a major blow to the council, but we are determined to strike back and continue our work," Rashid said. "Such an attack was expected, but it will not deter us."

A Ramadi police officer said Abu Risha had received a group of poor people at his home earlier in the day, as a gesture of charity marking the beginning of the Muslim holy month of Ramadan. The officer, speaking on condition of anonymity out of security concerns, said authorities believed the bomb was planted by one of the guests.

After the bombing, police announced a state of emergency in Ramadi and set up additional checkpoints throughout the city, Rashid said.

An Interior Ministry spokesman, Maj. Gen. Abdul-Karim Khalaf, said a committee would be sent from Baghdad to help Anbar police investigate the attack.

Khalaf said that after the first blast which killed Abu Risha, a car bomb exploded nearby.

"The car bomb had been rigged just in case the roadside bomb missed his convoy," he said. There were no casualties from the car bomb, he added.

The Interior Ministry swiftly ordered plans for a monument built to honor Abu Risha as a "martyr," Khalaf said. It would be build either at the explosion site, or at the center of Ramadi, he said.

It was not the first time Abu Risha and his colleagues have been targeted.

In February, the sheik escaped an assassination attempt by a suicide bomber. And in June, another bomber blew himself up in the lobby of Baghdad's Mansour Hotel during a meeting of U.S.-linked Sunni tribal leaders, killing 13 people and wounding 27.

Among those killed was the former governor of Anbar and sheik of the al-Bu Nimir tribe, Fassal al-Guood — a key ally of Abu Risha. A day later, Al Qaeda in Iraq claimed responsibility for the attack.