An explosion has caused injuries at an Indonesian police station, a day after local churches were attacked in three suicide bombings

Surabaya Goverment Handout/Andy Pinaria/Getty Images

A handout photo from the Government of Surabaya showing a bomb blast at Surabaya Pantekosta Center Church on May 13, 2018 in Surabaya, Indonesia.

• Injuries have been reported after a bombing at police headquarters in Surabaya, Indonesia on Monday.
• Monday's attack follows three suicide attacks targeting churches in Surabaya on Sunday that killed at least 13 and injured many more.
• The family of six who launched the suicide attacks reportedly tried to join Islamic State in Syria and were sent back to Indonesia.
• The family was tied to Jamaah Ansharut Daulah (JAD), an ISIS-inspired umbrella organization on the US State Department terror watchlist.

Injuries have been reported after a bombing at the police headquarters in Surabaya, Indonesia on Monday.

Spokesperson for the East Java Police Commissioner Frans Barung Mangera said the explosion occurred as part of a vehicular attack, CNN Indonesia reported.

Surabaya is Indonesia's second largest city.Surabaya is Indonesia's second largest city.

Preliminary reports from the Jakarta Post say 7 people were killed in the blast.

"Our personnel are identifying the victims. So far, we have accounted for seven people. We are still collecting data," Mangera told The Post.

Mangera added that Monday's attack may be related to the string of attacks which occured on Sunday, as similar explosive devices were used.

Suicide attacks targeted churches on Sunday

Monday's attack follows three suicide attacks targeting churches in Surabaya on Sunday that killed at least 13 and injured many others.

The family of six who conducted the suicide attacks reportedly tried to join Islamic State in Syria and were sent back to Indonesia.

Indonesia's police chief, Tito Karnavian, said at a news conference that the family had recently returned from Syria. "Five hundred people were deported from Syria; among them is this family," he said.

According to The Australian, Karnavian said the family had attempted to join ISIS but were arrested by Turkish authorities and were sent back to Indonesia. The family was tied to Jamaah Ansharut Daulah (JAD), an ISIS-inspired umbrella organization on the US State Department terror watch list.

Karnavian identified the father as Dita Futrianto, who was said to be the head of the Surabaya cell of JAD.

The explosions were carefully coordinated and were minutes apart.

Karnavian said the first bomb occurred in the parking lot of Sura­baya's Santa Maria Church, and is believed to have been detonated by the family's two eldest sons, aged 16 and 18, who approached the church on motorcycles rigged with explosives.

The second blast occured shortly after and is believed to have been detonated by their mother, Puji, and her two young daughters, aged 9 and 12. Karnavian said Dita dropped the three off at Diponegoro Indonesian Christian Church after outfitting them with explosives.

The final blast occured at Surabaya Center Pentecostal Church, after the father crashed into the church and detonated a bomb said to have been inside his car.

Two failed attacks were reported at two more churches, due to bombs failing to detonate, the Jakarta Post reported.

The police later discovered three bombs at the family's home, the New York Times reported, citing officials in Surabaya.

Islamic State has claimed responsibility for the attacks.

President Joko Widodo said the attacks were "a crime against humanity and has nothing to do with religion," and ordered police to break up militant networks.

In a statement, Australian Prime Minister Malcolm Turnbull condemned the "cowardly terrorist attacks" and said the Australian government "stands in solidarity with the government of Indonesia."