MANILA -- The bombing of a church service in the Mindanao State University gymnasium in Marawi City could be a retaliatory attack following a series of military operations against 3 terrorist groups in Mindanao, the head of the Philippine military said Sunday.

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Armed Forces of the Philippines (AFP) chief of staff General Romeo Brawner Jr. said the bombing of the church service came just 2 days after Western Mindanao Command forces killed 11 members of the terrorist group Dawlah Islamiyah including its declared emir, Abdullah Sapal, in Datu Hoffer Ampatuan, Maguindanao del Sur.

A day later, a separate military operation by Joint Task Force Orion also neutralized Abu Sayyaf group leader Mundi Sawadjaan, the suspected mastermind in the 2020 Jolo bombings.

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Finally, a third operation by the 103rd Infantry Brigade in Piyagapo, Lanao del Sur on Sunday also led to the neutralization of another terrorist leader.

"Dahil sa sunod-sunod na operation natin against the terrorist groups in the whole area of Western Mindanao dito sa Maguindanao, sa Lanao and sa Basilan, maaaring retaliatory attack 'yung nangyari kaninang umaga.
So that is one angle that we are looking into," Brawner said in a press briefing.

Defense Secretary Gilbert Teodoro earlier said at least 4 people were killed in the Sunday morning attack.

Fragments of a 60mm mortar from the improvised bomb used in the attack were recovered from the blast site.

Teodoro confirmed there were "strong elements of a foreign element" in the attack but refused to provide details.

Brawner said there were some similarities between the MSU bombing and the 2020 Jolo blasts.

The Philippine National Police has placed units in Mindanao on red alert while units in National Capital Region is on heightened alert as a precautionary measure.