JAKARTA - A family of six carried out suicide bombings at three churches in Surabaya in Indonesia's East Java province during Sunday mass on May 13, killing 13 people, according to the police.

The attacks took place at the Santa Maria Church in the Ngagel Madya area of Indonesia's second-largest and busiest city, the Surabaya Centre Pentecostal Church and the GKI Diponegoro Church.

East Java provincial police spokesman Colonel Frans Barung Mangera told reporters a total of 44 injured victims from the attacks have been sent to hospital. At least two of the injured were police officers on duty guarding the churches.

Islamic State in Iraq and Syria (ISIS) claimed responsibility for the attacks, the group’s Amaq news agency said, without providing any evidence.

“Three martyrdom attacks inflicts at least 11 deaths and 41 injuries of the churches’ guards and Christians in the city of Surabaya in East Java province in Indonesia,” the agency said in a statement that gave no further details.

Police chief General Tito Karnavian said ISIS-affiliated terror network Jemaah Ansharut Daulah (JAD) was behind the attacks and that all of the bombers were members of the same family.

JAD, or Jemaah Ansharut Daulah, is a terror group that first became known to Indonesian intelligence agencies in 2015, when almost two dozen extremist groups pledged allegiance to ISIS leader Abu Bakr al-Baghdadi.

A source told The Straits Times that the family is JAD founder Aman Abdurrahman's sleeper cell. Police are hunting those who provided the bombs, the source added.

Gen Tito said two brothers, aged 17 and 15, carried out the first bombing on the Santa Maria Church. They were on a motorcycle and carried the bomb on their lap.

Breaking: Video showing one of the Surabaya attackers riding a motorcycle into the grounds of a church and detonating a bomb. pic.twitter.com/X0DBrHB4p9 — Adam Harvey (@adharves) May 13, 2018

The second bombing, on the GKI Diponegoro Church, was carried out by the mother who had a belt bomb. She was accompanied by her two daughters, aged nine and 12. This was the first-ever suicide bombing by a woman in Indonesia.

Their father, who was on a car, staged the third bombing at Surabaya Centre Pentecostal Church.

A planned attack on a fourth church, Cathedral Church, was foiled with the arrest of a suspected bomber.

A police bomb squad also safely detonated an unexploded bomb that was discovered at the Surabaya Centre Pentecostal Church.

"All elements were quickly deployed to all vital places, especially places of worships. Three churches were attacked. Police arrested a person that was about to attack the otherwise a fourth target, the Cathedral Church. It has been foiled," Surabaya deputy mayor Mr Wisnu Sakti Buana told Elshinta radio.

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Elshinta cited eye witnesses and local residents as saying that the bombings all occurred at around 7am.

President Joko Widodo condemned the attacks as "barbaric", noting the use of children to facilitate one of the attacks.

At a news briefing alongside Gen Tito, Mr Joko said: “I have instructed police to look into and break up networks of perpetrators."

Graphic video footage and photographs from the site of the Santa Maria Church bombing showed several injured people lying prone on the ground and a boy covered in blood being carried away. The road outside the church was blocked. The bomb was probably detonated at the gate of the Santa Maria Church .

Meanwhile, Jakarta police spokesman Inspector General Setyo Wasisto said at a press conference that police killed four terrorists of the JAD terror network in Cianjur, West Java province, at around 2am on Sunday.

"We seized, among others, revolvers and a bow with arrowheads that contain explosive," Inspector General Setyo said.

"They were on their way to Brimob (Mobile Brigade Corps) headquarters. We tailed them from Sukabumi (West Java) and when we reached Cianjur, they were aware of being stalked and they attempted to flee. Our officers tried to stop them, had gunfights and managed to take them down."

The terrorists were identified as BCA (age 43), AR (32), HS (23) and BBN (whose age is unknown).

After the terrorists were killed in the exchange of gunfire, police arrested two terror suspects in West Java. One of them, known only by the initial G, was arrested in Sukabumi, while the other - initialled M - was apprehended in Cikarang.

Inspector General Setyo said police were investigating if the terrorists were linked to the Surabaya attacks. The four terrorists were from the JAD's greater Jakarta network.