Indonesia’s national police chief has said a suspect believed to be involved in explosions at a mosque inside a school complex, which caused dozens of injuries, was a student there, and an investigation is under way into his background and possible motive.

Listyo Sigit Prabowo said there were so far no deaths from the explosions in the capital, Jakarta. The incident happened during Friday prayers inside a school complex in Kelapa Gading, North Jakarta.

Prabowo said that one of two people in surgery is the suspected perpetrator. “The motive is still being investigated. We found toy weapons and some writings, which we are examining to understand the motive”, he added.

Police earlier had tried to tamp down speculation that the blast was an attack, with city police chief Asep Edi Suheri saying the cause was being investigated.

Witnesses reported hearing two loud blasts at about midday (05:00 GMT), just as the sermon had started at the mosque.

Fifty-five people, mostly students, were initially admitted to hospital with injuries ranging from minor to serious and including burns, Suheri said. Twenty remain in hospital care, with three suffering from serious injuries, he added.

Suheri said an anti-bomb squad that was deployed at the scene found toy rifles and a toy gun near the mosque.

“Police are still investigating the scene to determine the cause of the blasts,” he explained.

Local news channels showed footage of a police line around the school with ambulances standing by. Images of the mosque showed no extensive damage.

Worried relatives of the students gathered at centres set up at Yarsi and Cempaka Putih hospitals to seek information about loved ones. Parents told local television stations their children had wounds from being hit in the head, feet and hands by sharp nails and pieces of exploding objects.