Maj. Filemon Tan, spokesman for Western Mindanao Command, said in a statement that soldiers were closing in on positions held by the ISIL-linked group when a booby trap bomb went off at 6.20 a.m. (2220GMT Monday).

Tan said a scout ranger was killed on the spot while five of his companions were wounded and airlifted to Zamboanga City for medical treatment.

The ranger is the second fatality suffered by government troops in two weeks of operations on Basilan and Jolo islands, while 11 soldiers have been reported as wounded.

On Monday, the military claimed to have killed 40 Abu Sayyaf fighters and wounded 25 others. 

"The troops continue to assault enemy positions and neutralize ASG [Abu Sayyaf Group] elements," Tan said.

 In Sulu -- where the Jolo island offensive has been taking place since July 7 -- 22 militants have been killed and 16 wounded, while on Basilan 18 were killed and nine wounded, Western Mindanao Command said.

Since 1991, the Abu Sayyaf group -- armed with mostly improvised explosive devices, mortars and automatic rifles -- has carried out bombings, kidnappings, assassinations and extortions in a self-determined fight for an independent province in the Philippines.

Earlier this year, the group beheaded two Canadian hostages after ransoms failed to be paid.