Four worshippers lost their lives in a tragic explosion during Sunday Mass in the southern Philippines, leaving 42 others with minor injuries.

The incident took place in the gymnasium of Min-da-nao State University in Marawi (MSU), the largest Muslim city in the country.

Authorities suspect the involvement of the Daulah Islamiyah-Maute Group, which has links to the Islamic State.

Brig Gen Allan Nobleza, the regional police commander, suggested a possible retaliation for the recent encounter with the Philippine Army that resulted in the death of eleven group members.

President Ferdinand Marcos Jr condemned the blast as a "senseless and most heinous" act, attributing it to "foreign terrorists." He assured the public of justice and called for calm. Initial investigations point to a grenade or improvised bomb as the cause of the explosion.

Social media photos showed the aftermath in the MSU gymnasium with scattered chairs and minimal damage to the building. Many of the minor injuries have been treated, and Governor Mamintal Adiong Jr mentioned that numerous wounded individuals have been discharged.

Larger-than-usual crowds attended masses across the Philippines on Sunday, as it marked the start of Advent, the Catholic Church's four-week lead-up to Christmas Day.