Members of one family were behind a wave of blasts targeting three churches in Indonesia’s second city of Surabaya, police say.
At least 13 people were killed and dozens injured in the attacks.
A mother blew herself and two children up at one church, while the father and two sons targeted two others, police Chief Tito Karnavian said.
Sunday’s bombings, which the Islamic State group has claimed, are the deadliest in Indonesia since 2005.
Earlier in the day, Wawan Purwanto, of Indonesia’s intelligence agency, said an IS-inspired group, Jemaah Ansharut Daulah (JAD), was suspected to be behind the attacks
The father drove a bomb-laden car into the grounds of Surabaya Centre Pentecostal Church.
The mother and her two daughters – aged 9 and 12 – had bombs strapped to them and blew themselves up at Diponegoro Indonesian Christian Church.
The family’s sons – aged 16 and 18 – rode motorcycles into Santa Maria Catholic Church, and detonated explosives they were carrying. It was their attack that came first, at around 07:30 local time (00:30 GMT). The other two attacks followed five minutes apart, police said, according to the Jakarta Post.
TV pictures showed debris scattered around the entrance of one church.
Officials reportedly foiled attacks against other churches.
Visiting the scene of one of the bombings, President Joko Widodo described the attacks as “barbaric”, adding that he had ordered police to “look into and break up networks of perpetrators”.
Also on Sunday, police said they killed four suspected members of JAD in Cianjur, West Java, and arrested two others.