At least 13 people were killed and 40 were wounded after a family of six carried out suicide attacks against Christians attending Sunday services at three churches in Surabaya, Indonesia’s second-largest city, Reuters news reported.

Police said the family was among 500 Islamic State sympathizers who had returned to the country from Syria.

Homegrown militancy is rising in Indonesia, the world’s largest Muslim-majority country, Reuters reported.

“The husband drove the car, an Avanza, that contained explosives and rammed it into the gate in front of that church,” East Java police spokesman Frans Barung Mangera reportedly said at a press conference at the regional police headquarters in Surabaya.

The wife and two daughters carried out an attack at a second church, while two other children rode a motorbike and had a bomb across their laps, the report stated.

How old were the children?

The daughters were ages 12 and 9. The other two children, believed to be the man’s sons, were 18 and 16, according to the report.

The bombings were blamed on the Islamic State-inspired group Jemaah Ansharut Daulah. The U.S. State Department lists JAD as an “umbrella” terrorist organization with hundreds of Islamic State sympathizers in Indonesia.

The Islamic State claimed responsibility for the attacks in a message carried by its Amaq news agency, the report stated.

“This act is barbaric and beyond the limits of humanity, causing victims among members of society, the police and even innocent children,” President Joko Widodo said while visiting locations of the attacks.

Forensic and bomb squad officers searched the area and streets near the bombed churches were blocked by checkpoints and heavily-armed police, Reuters reported.

A television report showed black smoke and flames engulfing the front yard of a church. Hours after the attack, a large blast was heard as a bomb disposal squad dealt with a device, the report stated.

Was this related to a deadly prison standoff?

Days earlier during a 36-hour standoff, militant Islamist prisoners killed five members of an elite counter-terrorism force at a high security jail on the outskirts of Jakarta.

The church attacks are believed to be related to the standoff, Wawan Purwanto, a communication director at Indonesia’s intelligence agency, told Reuters.

“The main target is still security authorities, but we can say that there are alternative (targets) if the main targets are blocked,” Purwanto said.