The Mi-8 helicopter belonging to the Gazpromavia carrier, on an environmental monitoring mission over-flying a national park, was reported missing Wednesday after its crew failed to get in touch with ground control.
"At 11:25 a.m. Moscow time [8:25 a.m. GMT], another four bodies were found, bringing the total number of those killed to six," an emergency service official said.
A source in the local emergencies department said the crash may have been caused by poor weather conditions.
"The helicopter crashed into a mountain at a height of 700-900 meters," the source said. "The crash could have occurred due to poor weather conditions."
The local prosecutor's office said the helicopter had been certified as serviceable during a regular check before the flight.
A spokesman for the local prosecutor's office said a criminal case could be launched "for breaches of flight safety and aircraft operation rules" as soon as the circumstances surrounding the crash had been established.
The helicopter was carrying five crew members and one passenger.
