MANILA -- Authorities are looking into the possibility that foreign terrorists were involved in a bomb attack in Marawi City early Sunday morning, as investigators scramble to piece together clues from the crime scene.

Defense Secretary Gilbert Teodoro says that based on initial findings, there were strong indications of a foreign hand in the incident.

"(There is) indicia of foreign elements here we are looking into," Teodoro said.

He declined to mention specifics, citing the ongoing investigation.

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For his part, Armed Forces of the Philippines Chief of Staff Romeo Brawner noted certain similarities between the Marawi blast and the Jolo cathedral bombing in 2019.

Authorities then had mentioned the possibility of a foreign suicide bomber detonating one of the bombs which killed 20 people and injured more than a hundred people during mass.

He also noted the attack was possibly in retaliation for successive military strikes against top terror suspects in recent days.

On December 1, 11 members of Dawlah Islamiya were killed in a clash with the military in Datu Hoffer in Maguindanao, including the group’s purported leader Abdullah Sapal.

• Dawlah Islamiyah leader, 10 others killed in Maguindanao del Sur

This was followed by the killing of Abu Sayyaf leader Mundi Sawadjaan in an encounter in the waters off Tipo Tipo Basilan.

The military says Sawadjaan was the brains behind the Jolo Cathedral bombing in 2019.

Just this morning, another member of the Dawlah Islamiya was killed in Piagapo town in Lanao del Sur.

"We see some similarities, but we don't want to conclude. It may have to do with recent gains against the terrorist groups," Brawner said.

Authorities recovered fragments from a 60-mm mortar round at the blast site.

Of the four fatalities, three have already been identified. One casualty, a woman, has yet to be identified.

When asked whether she was a student, authorities declined to provide details.

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