Twenty-five people have been arrested in connection with the assassination of the leader of the U.S.-backed revolt by Sunni Arab tribesmen in Anbar province against al-Qaida in Iraq, a police official said Friday.

Those detained include the head of the security detail that was supposed to protect Sheik Abdul-Sattar Abu Risha, who was killed in a bombing Sept. 13, police Lt. Col. Jubeir Rashid said.

Rashid said the security chief, Capt. Karim al-Barghothi, told police that al-Qaida in Iraq offered him $1.5 million but that he was arrested before he could collect the money.

Two other bodyguards as well as some of Abu Risha's neighbors were also detained, Rashid said.

Abu Risha, who organized 25 Sunni Arab clans into an alliance against al-Qaida, died along with two bodyguards and a driver when a bomb exploded near his walled compound just west of Ramadi, 70 miles west of Baghdad.

Iraqi officials said the blast occurred in view of a guard shack and an Iraqi police checkpoint, raising suspicion that the killing was an inside job. The attack occurred 10 days after Abu Risha had met with President Bush in Anbar.

According to Rashid's account, al-Barghothi allowed a suicide car bomber into the compound minutes before Abu Risha was due to enter. The bomber pretended to be parking but detonated his explosives as the tribal leader's vehicle passed about 20 yards away, Rashid said.

Another suspect confessed to filming the operation, he said.

The details differed from earlier accounts that Abu Risha was struck by a roadside bomb just outside the compound.

The suspects were arrested the day after the bombing, Rashid added. He also said Abu Risha had given al-Barghothi money and a house as a wedding gift just six months before the attack, which he said was in the works for a month.

The al-Qaida front group the Islamic State of Iraq claimed responsibility for the assassination.

The U.S. military said this week that an al-Qaida-linked militant connected to his death and a plot to kill other tribal leaders had been arrested during a raid north of Baghdad. The militant was identified as Fallah Khalifa Hiyas Fayyas al-Jumayli, an Iraqi also known as Abu Khamis. The military did not immediately respond to comment about the latest arrests.

The assassination of Abu Risha dealt a setback to one of the few success stories in U.S. efforts to stabilize Iraq, but tribesmen in Anbar province have vowed not to be deterred in fighting the terror movement.

U.S. officials credit Abu Risha and allied sheiks with a dramatic improvement in security in such Anbar flashpoints as Fallujah and Ramadi after years of American failure to subdue the extremists. U.S. officials now talk of using the Anbar model to organize tribal fighters elsewhere in Iraq.