Updated

A suspected Al Qaeda in Iraq fighter believed responsible for the assassination of a U.S.-allied Sunni tribal leader in Anbar province was arrested north of Baghdad, the military said Sunday.

Fallah Khalifa Hiyas Fayyas al-Jumayli, an Iraqi also known as Abu Khamis, was seized Saturday in a raid west of Balad after intelligence reports linked him to the killing of Sheik Abdul-Sattar Abu Risha, the military said.

He was not believed to be acting alone and the search continued for other suspects, military spokesman Rear. Adm. Mark Fox said.

Abu Risha, 37, 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 against Al Qaeda in Iraq. He and three companions were killed in a bombing Thursday outside his heavily guarded compound in the Anbar capital of Ramadi.

The terror network issued a statement claiming responsibility for his death and vowed to hunt down others who turn against it.

Fox said al-Jumayli was accused of involvement in a plot to kill key leaders in the tribal alliance. He also reportedly was responsible for car bomb and suicide vest attacks in Anbar and was closely allied with senior Al Qaeda in Iraq leaders in the region west of Baghdad.

"We do not assess that he was operating alone, there is an investigation and continuing operations that are focused on ensuring that all people who were involved in this attack or in this murder will be detained," Fox said at a news conference.

U.S. troops raided three buildings while targeting al-Jumayli and three other suspects were detained, although the military did not provide specifics about the accusations against them.

Iraqi officials said the roadside bomb was just outside Abu Risha's walled compound in view of a guard shack and an Iraqi police checkpoint, raising suspicion that the killing may have been an inside job. Fox declined to comment on the speculation.

The Sunni revolt that Abu Risha spearheaded has led to a dramatic improvement in security in Anbar, a Sunni insurgent stronghold that had seen some of the fiercest fighting against U.S. forces since the war started in March 2003. The province remains unstable, but the decline in violence in Ramadi and other Anbar cities has been one of the major success stories for the U.S. mission in Iraq.

U.S. President George W. Bush met Abu Risha at a U.S. base in Anbar this month and praised his courage.