Col. Cirilo Tomas Donato, 104th Brigade commander, said the bomb exploded while Mussana Jamiri and his group were fleeing during a military operation in Akbar town in the southern island province of Basilan, where troops recently overran Abu Sayyaf encampments.

The Sun.Star news website also quoted Donato as saying that Jamiri’s group, who fled Tipo-Tipo town last week after government troops captured at least three of their hilltop strongholds, was involved in two fatal clashes earlier this week.

An encounter along the border of Akbar and Tuburan left three army scout rangers and one government militiaman dead Tuesday.

The same group was blamed for an ambush Wednesday night that killed one soldier and wounded another in Parangbasak village in Lamitan City.

Since 1991, the Abu Sayyaf -- 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.

It is notorious for beheading victims after ransoms have failed to be paid for their release.

The Abu Sayyaf is among two militant groups in the south who have pledged allegiance to ISIL, prompting fears during the stalling of a peace process between the government and the country's biggest Moro group that it could make inroads in a region torn by decades of armed conflict.