The death toll from a blast in the southern Philippine province of Sultan Kudarat has risen to two, with one of the injured in critical condition, authorities said on Wednesday.

Initial reports said one was killed and 35 others injured in the blast that rocked Isulan town at 8:35 p.m. (1235 GMT) on Tuesday. Authorities said on Wednesday one of those wounded died later at a local hospital.

Investigation was underway to get into the bottom of the deadly incident, authorities said.

No group has claimed responsibility for the blast yet. Authorities said there was no proof that Islamic State terrorists were behind the bombing.

Provincial police chief Noel Kinazo said Tuesday night that the homemade bomb went off at in front of a restaurant near a gas station along a highway. He said the improvised explosive device was placed under a parked motorbike by the road.

The explosion occurred while residents were celebrating a local holiday, he added.

The latest bombing occurred while Mindanao is under martial rule. The entire southern Philippine region has been under martial rule since May 2017 when terrorists occupied Marawi city for five months.