Surabaya, Indonesia: A family of six, including girls aged 12 and 9, launched suicide attacks on Christians attending Sunday services at three churches in Indonesia's second-largest city of Surabaya, killing at least 13 people and wounding 40, officials said.

Indonesia, the world's largest Muslim-majority country, has seen a recent resurgence in home-grown militancy. Police said the members of the family that carried out Sunday's attacks were among 500 Islamic State sympathisers who had returned from Syria.

"The husband drove the car, an Avanza, that contained explosives and rammed it into the gate in front of that church," East Java police spokesperson Frans Barung Mangera told reporters at the regional police headquarters in Surabaya.

The wife and two daughters were involved in an attack on a second church. At the third church, "two other children rode the motorbike and had the bomb across their laps", Mangera said.

The two daughters were aged 12 and 9 while the other two youngsters, thought to be the man's sons, were 18 and 16, the police said.

They blamed the bombings on the Islamic State-inspired group Jemaah Ansharut Daulah.

Jemaah is an umbrella organisation on a US state department terrorist? list and is estimated to have drawn hundreds of Islamic State sympathisers in Indonesia.

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

"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.

East Java police spokesperson Mangera said the attacks had killed at least 13 people and 40 had been taken to hospital, including two police officers. Reuters