ZAMBOANGA, Philippines ? FBI agents arrived Friday in the southern Philippines to investigate a bomb attack that killed three people, including an American Green Beret.

Philippine military officials blamed the Muslim extremist group Abu Sayyaf for Wednesday’s blast, which injured 24 people. They said the explosives were similar to those found in an unexploded bomb believed to have been planted by the guerillas on nearby Jolo Island in August.

National Security Adviser Roilo Golez said in a television interview that U.S. authorities were helping in identifying the type of bomb to determine if it contained a “signature” that could lead to any suspects.

FBI agents examined the blast site Friday, taking photographs, collecting evidence and trying to piece together the charred parts of the motorcycle in which the nail-laden bomb was stashed.

Gen. Ernesto Carolina, head of the Philippine military’s Southern Command in Zamboanga, said “all evidence points to the Abu Sayyaf as the perpetrators of this senseless bombing.”

The driver of the motorcycle was identified as an Abu Sayyaf member from a sketch based on witness accounts and his body. Police originally said the man had been killed, but later Chief Inspector Jose Bayani Gucela said the man left the area before the explosion.

Abu Sayyaf, which has been linked to the al-Qaida terror network, warned last week that it would mount attacks on civilian, military and U.S. targets in the Philippines to retaliate against an ongoing government offensive against Muslim rebels in the southern Philippines.

The body of slain American Green Beret, Sgt. 1st Class Mark Wayne Jackson, 40, of Glennie, Mich., was flown Thursday to Okinawa, Japan, along with another U.S. soldier injured in the blast. Jackson was assigned to the 1st Special Forces Group, at Fort Lewis, Wash.

An unidentified U.S. crime investigator measures a portion of a damaged vehicle outside a restaurant in the southern port city of Zamboanga, Philippines. FBI personnel arrived Friday in the Philippines to aid in the investigation of a powerful bomb that exploded and killed three people, including an American soldier, on Wednesday in Zamboanga.

The Green Berets, based across the street from the blast site at Camp Enrile, were part of a U.S. contingent of about 260 personnel deployed in support of Operation Enduring Freedom, which has helped train the Philippine military to fight the Abu Sayyaf.

A total of 272 American soldiers remain in the Philippines since the bulk of a 1,200-strong contingent began withdrawing after a counterterrorism exercise ended July 31.

U.S. military support helped Filipino troops decimate the Abu Sayyaf with a months-long offensive this summer on Basilan but is now fighting an Abu Sayyaf faction on another island nearby, Sulu.

Abu Sayyaf guerrillas seized 102 hostages, including three Americans, in a yearlong kidnapping spree. In a bloody army rescue attempt, American missionary Martin Burnham and Filipino nurse Ediborah Yap were killed, while Burnham’s wife, Gracia, was wounded but survived.