MANILA (Reuters) - The Philippine military believes it may have “neutralized” the remnants of an alliance of pro-Islamic State extremists, after the suspected death of the group’s de facto leader during clashes last week.

Forensic tests were being carried out to determine if one of four rebels killed on Thursday was Abu Dar, who security forces believe has led Dawla Islamiya, an alliance of pro-Islamic State fighters, foreign and Filipino, drawn from armed groups in the volatile Mindanao region.

Four soldiers were also killed during the fighting in Lanao del Sur province, which Islamic State claimed responsibility for on the mobile messaging service Telegram.

Regional army commander, Colonel Romeo Brawner, told ABS-CBN News that the death of Abu Dar would mean Dawla Islamiya had been “neutralized”.

Dawla Islamiya in 2017 occupied southern Marawi City for five months before its core leaders were reported killed by the military in air strikes and street battles, among them Isnilon Hapilon, Islamic State’s anointed “emir” in Southeast Asia. Abu Dar was seen in seized video footage sitting beside Hapilon.

If confirmed, his death would represent rare progress at a time of heightened alert across the predominantly Muslim areas of Mindanao, where a church attack by suspected suicide bombers in January killed 22 people and wounded more than 100, just days after a local referendum on autonomy returned an overwhelming “yes” vote.

Islamic State claimed responsibility for the church bombings, which the government believes were carried out by its supporters from another Mindanao group, Abu Sayyaf, which has a long history of criminal and extremist activity.