His father was a senior member of Al Qaeda in Iraq. His mother promised him they would meet again in paradise.

Details emerging in the investigation into a teenage suicide bombing near Fallujah on Sunday suggest the boy was dispatched by his family on the mission and took advantage of tribal ties to pass through tight security — raising concerns about infiltration within Sunni groups now allied with U.S. forces against extremists.

It also points to concerns that Al Qaeda and its backers are still committed to campaigns of revenge and intimidation against fellow Sunnis even as insurgents try to regroup after being driven from strongholds across central Iraq.

The 15-year-old attacker was carrying a box of candy at a gathering of tribal members to celebrate the recent release of a relative, Hadi Hussein, who had been let go after more than a week in U.S. custody, officials said. Hussein, his brother and four guards were killed in the blast.

The youth blew himself up in a reception area as Hussein was greeting well-wishers in the compound of Aeifan al-Issawi, a leading member of the Anbar Awakening Council — the first Sunni group to publicly turn against Al Qaeda in Iraq. Al-Issawi said he believed he was the target, but the bomber may have become nervous and detonated his explosives before he arrived.

"This is not the first time that we have been targeted by our relatives who live in the same area around us," said al-Issawi.

The Issawis represent one of the largest tribes in the province, which stretches west of Baghdad to the borders of Syria, Saudi Arabia and Jordan. The desert expanse provided a vast safehaven for Al Qaeda in Iraq until Sunni leaders became fed up with the group's brutal tactics and joined forces with the Americans against it.

Anbar was once considered a lost cause for the Pentagon. But it turned into one of the military's most vaunted success stories as the Sunni groups in Anbar helped stir similar uprisings against Al Qaeda in Sunni areas around Baghdad and elsewhere.

Marine Maj. Gen. Walter E. Gaskin, commander of the roughly 35,000 Marine and Army forces in Anbar, said earlier this month that levels of violence have dropped so significantly that the province will be returned to Iraqi control in March.

But the military has acknowledged concerns that some members could retain allegiances to Al Qaeda, particularly if they were former insurgents themselves.

Rear Adm. Gregory Smith, a U.S. military spokesman, said members were carefully screened and must pledge to renounce violence before being accepted.

"That's not to say that Al Qaeda has not found a way to infiltrate some members, some groups, that clearly could be the case," Smith said Sunday, referring to the Sunni movements.

The founder of the Sunni revolt in Anbar, Sheik Abdul-Sattar Abu Risha, was killed in a bombing near his compound on Sept. 13. Authorities arrested the head of his security detail who was accused of aiding the attackers.

Col. Faisal al-Zubaie, the city's police chief, identified the bomber on Sunday as Ali Hussein Allawi, who had traveled with his mother from the northern Sunni area of Samarra to visit relatives.

Allawi's father was considered a senior Al Qaeda in Iraq member in Anbar, but fled the area nearly a year ago after learning he was on a wanted list of insurgents compiled by the Awakening Council, al-Zubaie said. His current whereabouts are unknown.

Police rounded up 22 uncles and other relatives in the aftermath of the bombing, releasing all but five after questioning.

"During investigations those five gave confessions, including that the boy's mother told him 'God be with you and we will meet in paradise,"' al-Issawi quoted the suspects as saying.

Al-Issawi said police were investigating how Allawi had been armed, suggesting he must have received the explosives after arriving in the area to clear extensive checkpoints along the way.

"After the explosion, police forces detained uncles and relatives of this boy," al-Issawi said. "It is unbelievable that he came from Samarra with an explosive belt on him."

The implication that it was an inside job reflects the tangled relationships of the Anbar tribes, which are divided into a patchwork of clans that often have rival agendas.

Most of the clans within the Issawi tribe have turned against Al Qaeda, but a few remain loyal to the terror network.

The suicide attacker's mother — along with another woman believed by Iraqis to be another potential suicide bomber — took refuge in two houses in the area with other women from their clan. They have refused to come out despite orders by authorities via loudspeakers, prompting a standoff.

Authorities were hesitant to storm the buildings due to cultural sensitivities regarding use of force against women in a conservative Islamic society.

Many local residents remembered the family's connection to Al Qaeda in Iraq and warned authorities after the boy's return but claimed they took no action.

The attack against the tribal leaders came one day after three suicide bombers targeted a police station in the provincial capital of Ramadi. Guards killed one attacker, but two others detonated their explosives at the entrance, killing at least five officers, authorities said.

The U.S. military also said a Marine was killed Saturday during fighting in Anbar, the first U.S. combat death in the province since Oct. 8.