Another 35 people were wounded in the fire at the nursing home in the village of Kamyshevatskaya, in the Krasnodar Krai.
Krasnodar Krai prosecutor Leonid Korzhinek told journalists a criminal case has been opened. "A thorough investigation is under way now to determine the causes and conditions of the fire," Korzhinek said.
Authorities are considering a number of possible causes, including carelessness, a short circuit, or arson.
Emergency officials say multiple safety violations at the state-run home are responsible for the high death toll.
A night watchman ignored two fire alarms before reporting the blaze.
Firefighters arrived nearly one hour after receiving the call, because the nearest station is more than 50 kilometers away.
The flames were extinguished after several hours.
(compiled from agency reports)