Explosion in downtown Jakarta injures four people

Police declined to say whether the explosion on Wednesday in a densely populated area of the Indonesian capital was caused by a bomb.

The investigators did not find a timer nor a detonator at the scene, Jakarta police chief Unggung Cahyono said, adding that the police were still investigating all options.

Near the site, security forces found nearly 50 bags containing possibly dangerous material, according to Cahyono.

"It's like a firecracker, containing suspicious black powder, nails and stones," he told broadcaster TV One.

"It is possible that at the time of assembling, there might be a technical error which caused the explosion."

Injured by nails

One of the four people caught in the blast was hit by flying nails in the chest and suffered serious burns, while the other three only suffered slight injuries.

The police chief said that the three men are to be questioned soon.

Spokesman for Jakarta police, Martin Sitompul, also said the police found an object without detonator or cables, adding that it "seems to have exploded because of pressure."

Indonesia in the crosshairs

Indonesia has been combating various terror groups since the early 2000s, and has suffered a string of deadly attacks, notably the 2002 Bali bombings which killed 202 people.

In February, police discovered a crude chlorine bomb in a Jakarta shopping mall, which failed to detonate properly. Authorities later linked the attack to Indonesian militants, allegedly returning from fighting alongside the "Islamic State" in Syria.

dj/xx (AFP, Reuters)