MEDAN, Indonesia (AP) — Angry inmates set fire to an overcrowded prison on Indonesia’s Sumatra island during a riot that erupted Wednesday, officials said.

Hundreds of police and soldiers were deployed to take control of Kabanjahe prison in North Sumatra province, which is designed to house 193 inmates but now has more than 400, said Sri Puguh Budi Utami, director general of corrections at the Justice and Human Rights Ministry. She said it was guarded by only eight offic.ry.

Utami said the cause of the riot is still being investigated. A preliminary investigation showed it began after prisoners protested against the guards’ treatment of four inmates who were placed in isolation after being caught taking drugs into their cell, she said.

Other inmates, mostly arrested for drug offensives, joined the protest and it turned violent, but there were no reports of deaths, Utami said.

Television video showed prisoners in an open field under heavy guard by soldiers while police removed others from the prison compound. Black smoke billowed from a building, and burned office equipment and documents were scattered around the prison.

Local police chief Benny Hutajulu said eight fire trucks were mobilized to extinguish the fire and about 500 police and soldiers were deployed around the prison to prevent inmates from escaping.

Jailbreaks and riots are common in Indonesia, where overcrowding has become a problem in prisons that are struggling with poor funding and large numbers of people arrested in a war on illegal drugs.