Four people were killed and two others injured in a fire in a private drug treatment clinic in the Siberian city of Krasnoyarsk on Thursday, the Russian Emergencies Ministry said.
In the early hours of Thursday, the fire started on an area of 10 square meters in an office on the ground floor of a six-story residential building, where the clinic is located, it said.
The fire was put out and rescuers managed to evacuate 16 people, both residents of the building and patients of the clinic, it added.
The Russian Investigative Committee said in a separate statement that the cause of the fire was arson.
Investigators, while watching surveillance camera footage, found that one of the patients had set a fire in the interior of the building, causing the fire to spread rapidly through the ward.
The arsonist is not among the dead and the suspect is being confirmed, it said.