Philippine troops killed an undetermined number of suspected militants in a raid even as they took over a once formidable stronghold of the Abu Sayyaf extremist group deep in the jungles of southern Basilan in a bid to convert it into a base from where it will launch attacks against the group, the armed forces said.

Lt Gen. Roy Cimatu, chief of military forces in the south, said they are in the process of converting the Sampinit Complex into a military base.

The base, which Cimatu said is now the centre of anti-Abu Sayyaf operations on the island, houses elite units going after the rebel group.

These include the U.S.-trained Counter Terrorist Force, the army's First Scout Ranger Battalion and a contingent from the Fifth Marine Battalion Landing Team.

The complex is located on strategic high ground right in the middle of the island in Sumisip town.

The area, which was built by Japanese occupation forces during World War II, was used by the Abu Sayyaf as its base from where they launched attacks against government positions until last December when it was taken over by government forces for the second time since June 2000.

The complex is supported by a system of underground tunnels where the Abu Sayyaf hid their hostages, mostly children and school teachers, two years ago.

"It is only now that we are able to use the base for our operations. We can now supply the complex via helicopters, since roads leading to it are treacherous and can be used by the rebels for ambuscades," said an army officer.

The U.S. government had been giving military hardware – in the form of helicopters, cargo aircraft and infantry weapons – to the local armed forces in a bid to improve their fighting capability. Philippine troops have been engaged in a campaign to rescue two American hostages and a Filipino nurse from the Abu Sayyaf during the past six months.