A family of six 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.
This appears to be the worst attack to have been carried out by IS followers in Indonesia.
Mangera said three unexploded homemade bombs, two at the Pantekosta church and one at the Diponegoro church, were detonated by a bomb squad.
Head of Communications Division at National Police Headquarters Muhammad Iqbal said here that death toll from the bombings in the three Surabaya churches has risen to 13 as of the evening, with tens of others injured. "Suddenly she hugged a civilian then (the bomb) exploded", said a civilian guard named Antonius.
At Santa Maria, shattered glass and chunks of concrete littered the entrance. Rescue personnel treated victims on a nearby field while officers inspected wrecked motorcycles in the parking lot that were burned in the explosion.
Later on Sunday night a bomb killed three people and wounded two, all from the same family, who occupied the fifth floor of a low-priced Surabaya apartment complex, East Java police spokesman Frans Barung Mangera said.
Back in 2002, 200 people were killed in two bombings carried out by al-Qaeda militants on the island of Bali, a popular spot for tourists.
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Tito said that terrorists' sleeping cells in Indonesia now started to wake up following the recent riot incited by terrorist inmates in police's high security prison that killed five police and one terrorist. Investigators believe that the family was not only linked to the Surabaya chapter of Jemaah Ansharut Daulah, a terrorist network with links to Islamic State (IS), but that they were among 500 Indonesians recently returned from Syria who had gone to the Middle East to fight with IS and that they had spent some time with the terrorist group learning about terrorism tactics and bomb making.
He said the wife and two daughters in the family were involved in an attack on a second church, while at the third church, "two other children rode the motorbike and had the bomb across their laps".
In May previous year, suicide attacks which killed three policemen and wounded a dozen more at a busy Jakarta bus station were also claimed by IS.
Police have closed off all three locations as they investigate.
The incident is estimated to be the deadliest attack in recent years to hit the world's biggest Muslim-majority nation. He said two police officers were among a total of 41 wounded. Jemaah Islamiyah, the network responsible for the Bali attacks, was destroyed by a crackdown from Indonesia's counterterrorism police with US and Australian support.
Christians, many of whom are from the ethnic Chinese minority, make up about 9 percent of Indonesia's 260 million people.