“The most important thing for all is to stay vigilant, be careful. If there is anything suspicious, report it to police,” said Jokowi on the sidelines of a visit to Cirebon, West Java, on Thursday, as quoted by kompas.com.

(Read also: Firecracker explodes near Catholic church in Ambarawa)

Jokowi explained that the National Police, particularly its counterterrorism squad Densus 88, and the National Counterterrorism Agency (BNPT) had undertaken efforts to crack down on terrorist groups.

However, he added that groups with radical ideology still existed in Indonesia. “Managing things like that [radical groups] is not easy,” said Jokowi.

The explosion caught members of the congregation by surprise as it occurred while they were preparing the church for the celebration of Good Friday.

Firecrackers and several empty bottles confiscated by police in connection with the explosion near a Catholic church in Ambarawa, Central Java, on Thursday.(Courtesy of the National Police/File)

“I originally thought it was the sound of firecrackers, but I wondered why [the sound] occurred repeatedly. After I checked the south gate, there were fires and many bottles,” said Eko Setia Budi, 50, Santo Yusuf’s sexton.

Police reacted swiftly by arresting 37-year-old local resident Muhammad Fahrudin, the alleged perpetrator of the incident, which causes no casualties.

According to residents, Fahrudin suffers from a mental illness. (mrc/bbs)