Two bombs exploded just minutes apart at a Roman Catholic cathedral in the southern Philippines, killing at least 20 people and wounding more than 100 others during a Sunday Mass.

The Islamic State has claimed responsibility for the bombings, the group’s Amaq news agency said Sunday, hours after the attack. The second bomb reportedly went off as first responders arrived at the Cathedral of Our Lady of Mount Carmel, located in Jolo.

The Armed Forces of the Philippines ecured the area of the blast and transported injured victims to the nearest medical facilities. Regional officials said all casualties were immediately evacuated out of the area, CNN reported.

Witnesses said hat the first bomb inside the cathedral sent churchgoers rushing outside. While police and army troops tried to enter the building, the second blast went off, causing more deaths and injuries.

Jolo has long been a base for Islamist militants, most notably those of the small Abu Sayyaf group, who are known as one of the most violent Islamic separatist groups in the Philippines.

At least 20 people killed as bombs target Sunday Mass in Philippines cathedral