By Ainur Rohmah

TUBAN, Indonesia

Indonesian police have arrested a suspect following an explosion outside a church in East Kalimantan province that left four children injured.

The police chief of provincial capital Samarinda told Anadolu Agency that they are questioning a 32-year-old man -- identified by his initial J -- on suspicion that he threw an explosive after the church congregation finished worship at around 10.00 a.m. (0300GMT) Sunday.

“Four victims [were injured] and four motors were burning in the church yard,” Commissioner Setyo Budi said. “A perpetrator has been arrested and is being questioned. He is injured but still conscious."

Budi refused to comment on whether police believe the suspect is affiliated to any extremist groups.

The national police chief later told reporters that the suspect had previously been in prison in relation to a series of bombings in Jakarta in 2011.

"The attacker was a prisoner over the terror bombing at the Research Center for Science and Technology Development and related to the ‘book bombings’," detik.com quoted Tito Karnavian as saying.

In 2011, authorities accused a terrorist network of carrying out a series of bombings in which packets of books containing explosives were sent to prominent figures in the capital.

That same year, a bomb exploded in front of the Ministry of Research, Technology and Higher Education’s Research Center for Science and Technology Development located in Serpong outside of Jakarta.

No one was injured by the explosives.

Indonesia has been on alert against extremist activities over the past year, further heightening security measures after an attack in Jakarta killed eight people -- including four Daesh-linked assailants -- in January.

In August, an 18-year-old arrested after trying to kill a priest in a North Sumatran church was reported to have claimed to have been inspired by love for Daesh's leader in Syria and an attack by Daesh-linked knifemen in France.