Bomb attacks killed two people on Tuesday on a restive southern Philippine island where Al Qaeda-linked militants are known to operate, police said.
The attackers apparently targeted a government building and a church in Isabela city on Basilan island with two home-made bombs, then shot at civilians, provincial police chief Senior Superintendent Antonio Mendoza said.
"Two were killed in the initial blast", Mendoza told reporters in the port city of Zamboanga, a short ferry ride across the strait from Basilan.
The first bomb went off about 10:30 am (0230 GMT) outside an education department building, according to Mendoza. He said the second, rigged to a motorcycle left near a Roman Catholic church, went off minutes later as security forces chased after the suspects.
"It heavily damaged the church", he said, but added no-one was wounded in that blast.
"The men were shooting at civilians as they fled towards a forested area", Mendoza said.
Authorities said they were yet to determine who was behind the attacks.
Several armed Muslim groups operate on the impoverished island of nearly half-a-million people, including the Abu Sayyaf, which is blamed for the country's worst terrorist attacks.
The country's police chief Jesus Verzosa had earlier warned the Abu Sayyaf was increasingly using improvised bombs in its attacks after defeats on the battlefield.
In March, an Abu Sayyaf landmine wounded three Filipino soldiers on Basilan.
Two roadside bombs killed a Filipino soldier and wounded 12 other people in near-simultaneous attacks also on Basilan island in February.
In September last year, an improvised explosive device blamed on the Abu Sayyaf killed a Filipino Marine and two US soldiers on a training mission on neighbouring Jolo island.