A massive fire at a drug rehabilitation centre in northern Iran has killed at least 32 people and injured 16, Iranian media reported on Friday.

Initial investigation showed that a heater in the opium rehab camp in Langarud in the Caspian Sea province of Gilan was the cause of the fire that spread to the rest of the centre, the province’s deputy governor was quoted as saying by the semi-official Fars news agency.

“The manager and other possible culprits have been arrested so that the cause of the incident is more accurately determined,” the Tasnim news site said.

According to the United Nations Office on Drugs and Crime, Iran has one of the most severest addiction problems in the world.

It lies on the main trafficking route for poppy, the source of opium and heroin, from Afghanistan to Western Europe.