The one-story brick-and-wood hospital building housed patients with severe mental disorders, Health Ministry officials said. An Emergencies Ministry official said the fire started in a wooden annex and then spread to the main brick building, which had wooden beams.
Health Minister Veronika Skvortsova said that half of the patients took sedatives at night. She insisted that the patients were not tied to their beds and were not given any medication that would leave them unconscious and unable to escape.
At least 29 people were burned alive, said Irina Gumennaya, a spokeswoman for the federal Investigative Committee.
Investigators said the 38 dead included 36 patients and two doctors. They said a nurse managed to escape and save one patient, while another patient got out on his own. The Emergencies Ministry also posted a list of the patients indicating they ranged in age from 20 to 76. Gumennaya told Russian news agencies that most of the people died in their beds.
Moscow region Governor Andrei Vorobyev said some of the hospital windows were barred. Gumennaya cited the surviving nurse as saying that the doors inside the hospital were not locked.
Investigators said they are looking at violations of fire regulations and a short circuit as possible causes for the blaze that engulfed the hospital in the Ramensky settlement, some 85 kilometers (53 miles) north of Moscow.
Vadim Belovoshin of the Emergencies Ministry said that it took firefighters an hour to get to the hospital because a ferry across a canal was closed and they had to make a detour.
Vorobyev told Russian state television that the fire alarm seems to have worked, but the fire spread too quickly.
Skvotsova told the state television said that the hospital had all the necessary fire equipment, but conceded mental hospitals should be better equiped for emergencies than the current law requires.
President Vladimir Putin called for a thorough investigation into the deadly fire and asked regional authorities to pay more attention to safety regulations.
Russia has a poor fire safety record, with about 12,000 deaths reported in 2012. In January, a fire in an underground parking lot killed 10 migrant workers from Tajikistan who were working and living there. In a similar incident in September, 14 Vietnamese workers were killed by fire at a clothing factory near Moscow.
In one of the most high-profile cases of negligence, more than 150 people died in a night club in the city of Perm after a pyrotechnic show ignited a wooden ceiling.
