Local officials have said that two bike-borne assailants were responsible for the attack.

"Police officers were injured in the explosion, which occurred at 08:50 local time (01:50 GMT), but the extent of casualties was not immediately clear," BBC reported.

The Islamic State has said that it was behind the attacks.

The death toll in the church bombings in Indonesia's Surabaya city has touched 13.

According to local police, a single family was behind the attack, which has been deemed as the deadliest in more than a decade's time.

The family consisted of six people, including a 9-year-old girl.

According to reports, the mother and her two daughters were involved in a suicide attack at a church, while the father and his two sons attacked two more churches.

Local officials have said that the family may have spent some time with the Islamic State in Syria and were related to a local IS-inspired network, Jemaah Ansharut Daulah (JAD).

The officials added that the father drove a bomb filled car into the premises of Surabaya Centre Pentecostal Church.

The mother and the daughters, who had bombs strapped to them, attacked the Diponegoro Indonesian Christian Church.

The daughters were aged 9 and 12, while the sons were 16 and 18 years old, respectively.

They reportedly rode motorcycles while attacking Santa Maria Catholic Church.

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