The suspects holed up on the island of Umapoy in Tawi-Tawi were allegedly involved in the abduction of a group of Indonesian, Filipino and Malaysian resort workers from the nearby Malaysian state of Sabah last year.
Armed Forces Southern Command chief Lt. Gen. Roy Kyamko directed the anti-terror unit based in Tawi-Tawi to intensify the operations following the release of four of the hostages.
Marines and Navy Special Forces units raided the island, on the southeast edge of the Tawi-Tawi group near the sea border with Sabah, on Tuesday following a tip-off that the Abu Sayyaf kidnappers had hid their hostages there for a time, task force commander Navy Capt. Feliciano Angue said.
Navy gunboats and attack helicopters sank two motorboats belonging to fleeing gunmen and intercepted at least one other vessel, he told reporters.
The raiders recovered the bodies of three suspected Abu Sayyaf kidnappers and arrested seven others. The rest of the 50-odd group escaped at sea but pursuit operations are continuing, Angue said.
"There could be more casualties as we have used overwhelming firepower just to penetrate the area of the Abu Sayyaf," according to Angue, talking from his base in Panglima Sugala, Tawi-Tawi.
"The island camp is well fortified as we have to move in walking 30 minutes... in shallow waters without any cover and exposed to enemy hostile fire," the Navy officer said.
The Abu Sayyaf, allegedly linked to the al-Qaeda network of Islamic militants, is deemed a "foreign terrorist organization" by the United States. The group has mounted spectacular kidnappings of American and European tourists and missionaries in the past.
The Abu Sayyaf gunmen on Umapoy "are all implicated in the kidnapping of the Borneo hostages," Angue told reporters.
He said some of the group had relocated to Umapoy after having been displaced by military operations on their traditional holdouts on the islands of Jolo and Basilan.
The gunmen forcibly displaced the fishermen who lived in houses on stilts on the coast of the tiny island, he said. "They kept their six hostages here for a time."
The hostages — three Indonesians, two Filipinos and a Malaysian — were snatched from a resort on the Malaysian section of Borneo island in October.
The Indonesian captives and a Filipino were released Monday. The freed hostages told the Malaysian authorities one of the hostages had died in captivity while another escaped late last year.
The freed hostages were identified as Indonesians Amir Nangi, 50, Arsyad Sagoni, 45, Suwito, 23, and Filipino Azarah Sariban, 50. Two of the victims were said to be very ill.
"We have received reports that the suspects brought their captives from Lahad Datu to that (Umapoy) island," Angue said, referring to the six workers taken from Eco-Paradise Farm last Oct. 5.
Angue said the naval operation was coordinated with the Malaysian authorities, who arrayed their navy vessels along the sea border just 10 nautical miles away to prevent the kidnappers escaping to Malaysia.
He said they have reason to believe the Abu Sayyaf they encountered could have given refuge to the group of Mujib Susukan and Ghalib Andang, who led a raid of the Sipadan resort in Malaysia in 2000, taking mostly European tourists.
Meanwhile, a Filipino soldier was killed and five others were injured in a grenade blast inside an Army base in this southern port city before dawn Tuesday, the military said.
The authorities are investigating the cause of the blast, which occurred in the barracks of the First Scout Ranger Regiment, said military spokesman Lt. Col. Renoir Pascua. — AFP, Roel Pareño