At least 27 people were killed and 77 were injured on Sunday in twin explosions in a Roman Catholic cathedral on a southern Philippine island where Islamist militants are active, AP reported.

Oscar Albayalde, the country’s national police chief, said the first bomb went off in the cathedral in Jolo during a Sunday mass, followed by a second explosion outside the compound while the security forces were responding to the attack. The dead include troops and civilians, he added.

Photographs on social media showed debris and bodies on a busy street outside the Cathedral of Our Lady of Mount Carmel, which has been hit by bombs in the past.

“I have directed our troops to heighten their alert level, secure all places of worships and public places at once, and initiate pro-active security measures to thwart hostile plans,” said Defence Secretary Delfin Lorenzana.

The Abu Sayyaf group, which has been designated as a terrorist organisation by the United States and the Philippines for its alleged links to the Islamic State group, has a presence on the island. The group is responsible for a spate of bombings, kidnappings and beheadings. Though the group has not claimed responsibility, “the primary suspect is still ASG”, said Lieutenant General Arnel Dela Vega, the chief of the Western Mindanao Command.

This is not the first time that the church has been attacked, reported The New York Times. In 2010, two separate grenade attacks occurred at the church, though no one was reported hurt. Three years later, two churchgoers were wounded in a similar attack.