A family of six carried out attacks on three churches in Surabaya city of the East Java province of Indonesia on Sunday, killing at least 13 people and injuring nearly 40, the BBC reported quoting the police.

National police chief Tito Karnavian told AP that the father detonated a car bomb, two sons – aged 18 and 16 – used a motorcycle for their attack and the mother was with the daughters – aged 12 and 9 – for her attack. He said that the family had recently returned to Indonesia from Syria. The police said the blasts all occurred within 10 minutes of each other, with the first around 7.30 am local time (6 am Indian Standard Time), AFP reported.

The explosions targeted the Santa Maria Catholic Church, Christian Church of Diponegoro and the Pantekosta Church, according to BBC. The explosion at Santa Maria church killed four people and two people were killed at each of the two other churches, said East Java police spokesperson Frans Barung Mangera. At least two people later died at a hospital. A planned attack on a fourth church, Cathedral Church, was foiled with the arrest of a suspected bomber, according to The Strait Times.

A witness told AP that the woman who carried out the attack at the Christian Church of Diponegoro was carrying two bags. “At first officers blocked them in front of the churchyard, but the woman ignored them and forced her way inside,” said the witness, who identified himself as Antonius. “Suddenly she hugged a civilian and then [the bomb] exploded.”

The Islamic State Group has also claimed responsibility for the attacks.

Mangera said three unexploded homemade bombs, two at the Pantekosta church and one at the Diponegoro church, were detonated by a bomb squad.

Meanwhile, national police spokesperson Setyo Wasisto said the police shot dead four suspected militants and arrested two others on Sunday in West Java towns. However, it is not confirmed if the shootings were related to the attacks on the churches.

Indonesian President Joko Widodo termed the attacks as “barbaric”, reported Reuters. At a press briefing, Widodo said that in one of the attacks, two children were used in the bombing.

Indonesia’s Foreign Minister Retno Marsudi took to Twitter to condole the victims’ families with the hashtags #UnitedAgainstTerrorism and #WeAreNotAfraid.