A soldier and a militant were killed in two successive firefights at dawn that allowed troops to rescue the two Indonesians in the mountainous hinterlands off Panamao town in Sulu province, said Lt. Gen. Cirilito Sobejana.

Troops, backed by rocket-firing helicopters, were pursuing the militants in an effort to rescue the third Indonesian, he said.

"We have cordoned the area so we are very optimistic that we will recover the remaining Indonesian," Sobejana told reporters.

The Indonesian fishermen were kidnapped at gunpoint by the ransom-seeking militants in September off Malaysia's Sabah state and taken to their jungle bases in Sulu despite tighter security by Malaysian, Philippine and Indonesian forces to prevent such abductions along their maritime border.

Military offensives against militants such as the Abu Sayyaf have reduced abductions in recent years, but they continue to occur. Abu Sayyaf gunmen have staged kidnappings in and off Sabah in recent years, sparking a regional security alarm.

The rescue of the Indonesians came after the military inflicted successive battle defeats recently to the Abu Sayyaf, which is blacklisted as a terrorist organization by the U.S. and the Philippines.

Troops have killed a "high-value" but little-known Abu Sayyaf commander, Talha Jumsah, near Sulu's mountainous Patikul town. Jumsah acted as a key link between the Islamic State group and local jihadis and helped set up a series of deadly suicide attacks in Sulu this year, officials said.

The Abu Sayyaf emerged in the late 1980s as an offshoot of the decades-long Muslim separatist insurgency in the south of the largely Roman Catholic nation. After losing its commanders early in battle, the Abu Sayyaf rapidly degenerated into a small but brutal group blamed for ransom kidnappings, beheadings and other acts of banditry. Most of its militant factions have pledged allegiance to the Islamic State group.