Philippine authorities vowed to crush the "terrorists" after two double blasts at a church church in the south of the country on Sunday, killing at least 20 people.
Eighty-one people have been wounded in one of the bloodiest attacks in the past few years in a region plagued by long-standing instability.
The bombings are a state of hope and optimism in the region after Friday's announcement of the approval of a self-governing zone in the southern Philippines by 2022.
Officials said the first blast took place inside the cathedral on the island of Jolo in Sulu province, followed by a second explosion outside, while security forces rushed to the scene.
"The enemies of the state have brazenly challenged the government's ability to ensure the safety of the people in this region," said Salvador Panilo, spokesman for Philippine President Rodrigo Duterti. "The Armed Forces of the Philippines will be challenging and will crush those criminals who have no God."
No one has claimed responsibility, but the police suspect they are behind the execution of the militant Abu Sayyaf group, which has sponsored a terrorist group.
"They want to review the force and spread chaos," Reuters quoted National Police Chief Oscar Albayald as saying, adding that the Abu Sayyaf group was the main suspect in the attack.
Jolo Island is the stronghold of the Abu Sayyaf, which is profiting from piracy and kidnappings, and successive governments have failed to dismantle it. The group, which is active in the west of Mindanao, cut off the heads of a number of foreign prisoners before, when the ransom it requested was not paid.
