Fourteen people were wounded on Palm Sunday when two suicide bombers blew themselves up outside a Catholic church in the Indonesian city of Makassar.
The attack at Sacred Heart Cathedral came on Palm Sunday, the first day of the Easter Holy Week.
According to the police, the congregation had been inside the church on the island of Sulawesi at the time of the explosion.
The bombers struck just as the mass was ending.
National police spokesman Argo Yuwono said authorities were looking into which radical networks the bombers came from.
They were also probing whether the attack was linked to recent arrests of suspected militants.
In January, a counter-terrorism unit raided a militant hideout in Makassar and killed two men suspected by police of involvement in twin bombings at a Philippine church in 2019 that killed more than 20 people.
Father Wilhemus Tulak, a priest at the church, told Indonesian media that a suspected bomber tried to enter the church grounds on a motorbike, but had been stopped by a security guard.
Security camera footage showed a blast that blew flame, smoke and debris into the middle of the road.
Police did not say who might be responsible for the attack and there was no immediate claim of responsibility.
Police blamed the Islamic State-inspired Jamaah Ansharut Daulah group for suicide attacks in 2018 on churches and a police post in the city of Surabaya that killed over 30 people.
Boy Rafli Amar, the head of the country’s National Counterterrorism Agency, described Sunday’s attack as an act of terrorism.