Six people were wounded on Saturday when a bomb went off in a church during Christmas mass on a southern Philippine island known as a hotbed of Islamic extremism, the military said.
Military officials would not immediately name any suspects in the blast on Jolo island but the island is a known bastion of the Abu Sayyaf, a group linked to the Al-Qaeda network.
"The explosion occurred at around 7:15 in the morning while the mass was going on. Six people were slightly wounded in the explosion," military spokesman Lieutenant Randolph Cabangbang said.
Among those wounded was the priest officiating the mass, he added.
Police investigators were searching the site for clues as to who might be responsible, he said.
The Abu Sayyaf, a gang of self-styled Islamic militants founded in the 1990s with seed money from Osama bin Laden's network, has long used the mostly-Muslim island of Jolo as a base, carrying out kidnappings and bombings.
It is believed to have carried out the worst terror attacks in Philippine history including the bombing of a passenger ferry in Manila Bay that killed more than 100 people in 2004.
It has also kidnapped many foreigners and Filipino Christians, hiding them in the jungles of Jolo and other southern islands.
US forces have been deployed in the southern Philippines since 2002 to train local troops in hunting down the Abu Sayyaf.
A roadside bomb believed planted by the Abu Sayyaf killed two US soldiers on Jolo in September last year.