The attack took place on Sunday at a time the congregation was inside the church on the island of Sulawesi, just as the mass was ending.

The two suspects were the only fatalities.

National Police Chief General Listyo Sigit Prabowo told reporters that the two attackers are believed to have been members of the armed group Jemaah Anshorut Daulah (JAD), which has pledged allegiance to ISIS and was responsible for deadly suicide bombings on Indonesian churches in 2018.

“I strongly condemn this act of terrorism and I have ordered the police chief to thoroughly investigate the perpetrators’ networks and tear down the networks to their roots,” President Joko Widodo said in an online broadcast following the attack.

He said the explosion occurred at about 10:30am (03:30 GMT) and that none of the worshippers was killed. Security camera footage showed a blast that blew flame, smoke and debris into the middle of the road. Makassar Mayor Danny Pomanto said the blast could have caused far more casualties if it had taken place at the church’s main gate instead of a side entrance.

“Whatever the motive is, this act isn’t justified by any religion because it harms not just one person but others, too,” Yaqut Cholil Qoumas, Indonesia’s religious affairs minister, said in a statement.

Gomar Gultom, head of the Indonesian Council of Churches, described the attack as a “cruel incident” as Christians were celebrating Palm Sunday, and urged people to remain calm and trust the authorities. Indonesia’s deadliest attack took place on the tourist island of Bali in 2002, when bombers killed 202 people, most of them foreign tourists. In subsequent years, security forces in Indonesia scored some major successes in tackling armed groups but, more recently, there has been a resurgence of violence.