BAGHDAD – The most prominent figure in an American-backed revolt of Sunni sheiks against Al Qaeda in Iraq was killed today by a bomb planted near his home in Anbar province, 10 days after he met with President Bush, police, and tribal leaders said.

Abdul-Sattar Abu Risha was leader of the Anbar Salvation Council, also known as the Anbar Awakening — an alliance of clans backing the Iraqi government and American forces.

Officials said his assassination would be a huge setback for American efforts in Iraq, because it sends a message to others who are cooperating with coalition forces or thinking about cooperating against Al Qaeda.

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, a supervisor of Anbar police, Colonel Tareq Youssef, said.

A spokesman for the top American commander in Iraq, General David Petraeus, confirmed the report.

“It is confirmed that the sheik and two of his bodyguards were killed today near or outside his home,” Colonel Steven Boylan said in an e-mail from Washington, where Mr. Petraeus testified before Congress this week on recent successes in Anbar province.

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

Abu Risha was among a group of tribal leaders who met with Mr. Bush on September 3 at al-Asad Air Base in Anbar province.

It was not the first time that Abu Risha has been targeted. A suicide bomber tried to kill him on February 19. That same day, gunmen ambushed a minivan on the main highway from Baghdad to Anbar and killed all 13 passengers who were accused of opposing Al Qaeda in Iraq.

In June, a suicide bomber blew himself up in the lobby of Baghdad’s Mansour Hotel during a meeting of American-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.

“It is a major blow to the council, but we are determined to strike back and continue our work,” a senior member of Abu Risha’s group, Sheik Jubeir Rashid, said. “Such an attack was expected, but it will not deter us.”

He said the bombing took place at 3:30 p.m. as Abu Risha was returning home.

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 visitors.

An Interior Ministry spokesman, Major General Abdul-Karim Khalaf, said that after the first blast that killed Abu Risha, a car bomb exploded nearby.

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

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

Anbar police were investigating the attack, and the Interior Ministry would send a committee to assist, Mr. Khalaf added.

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,” he said. “Such an attack was expected, but it will not deter us.”

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