The Philippine National Police (PNP) chief said on Sunday that the death toll climbed to 19 in the twin explosions at a church in Sulu Province of the southern Philippines on Sunday morning.
The Philippine authorities said among the dead were army soldiers.
PNP chief Director General Oscar Albayalde said 48 people were reported injured in the blasts.
The twin explosions happened after around the 8:15 a.m. mass at the Jolo Cathedral. Albayalde said one bomb went off inside the church while the other one outside of the church. "It went off one minute apart," he said.
The victims are mostly churchgoers.
"We strongly condemn the bombing at the Jolo Cathedral in Jolo, Sulu at 8:15 a.m. today just before the start of the holy mass that killed and wounded soldiers and civilians," Philippine Defense Secretary Delfin Lorenzana said in a statement.
He said the Armed Forces of the Philippines has immediately secured the explosion area and transported the casualties to the nearest medical facilities, including air evacuation of some victims to Zamboanga City for further medication and evaluation.
"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," Lorenzana said.
"As we convey our sincerest condolences to the families and friends of the victims and offer our sympathy to the peace-loving people of Sulu who are severely affected by this dastardly act, we assure our people that we will use the full force of the law to bring to justice the perpetrators behind this incident," he added.
Lorenzana urged the public to be more vigilant and cooperative with the authorities in reporting any security-related concerns.
"We also urge everyone to remain calm and avoid spreading panic in our respective communities to deny terrorism any victory," Lorenzana said.
The bombings took place days after the ratification of the Bangsamoro Organic Law (BOL), a new law that paves the way for the creation of a wider autonomous region for Muslim Filipinos in Mindanao.
Jolo rejected the BOL in a plebiscite on Monday but the law was ratified due to a landslide win in other predominantly Muslim provinces, including Lanao del Sur and Maguindanao.
The Commission on Elections said on Friday that the BOL was "deemed ratified" after getting more than 1.5 million favorable votes.
