At least 19 people, including children, died when a MI-8 helicopter crashed in the nearly impassable taiga in eastern Siberia, an aviation committee has said.
The Moscow-based committee, citing the surviving crew, said on Tuesday 19 of the 28 people on board were killed, but the emergencies ministry refused to confirm the toll.
The accident is the latest disaster to hit Russia's accident-prone aviation industry.
The ministry said rescue teams had difficulty reaching the crash site in the mountainous woods of the northern Yakutia region due to bad weather.
Some 240 rescuers and eight aircraft have been dispatched to the area.
"There were three crew members and 25 passengers on board," the Interstate Aviation Committee said in a statement. "Nineteen people died, the aircraft burnt down."
Of the 25 passengers, 11 were children, officials said without providing further details.
The accident apparently happened when the Polar Airlines helicopter performed a hard landing in poor weather, 45km northwest of the small town of Deputatsky in Yakutia.
The first deputy head of the Interstate Aviation Committee, Alexander Filatov, told the AFP news agency he had been notified of the death toll through a telegram from aviation officials in Yakutia, who were able to communicate with the crew after the crash.
But a spokeswoman for the emergencies ministry, Irina Rossius, said it could not give a toll until rescue teams were on the ground.
A spokesman for the regional government in Yakutia, Afanasy Yegorov, said the helicopter was performing a regular passenger flight from the town of Deputatsky to the town of Kazachye and was flying over a mountain range when a downward stream of air pushed it to the ground.
With weather conditions in the area rapidly deteriorating, the emergencies ministry said another MI-8 helicopter flying from the town of Tiksi was ordered to fly back.
But a plane carrying rescue workers and medics has already been able to land in the town of Deputatsky, the ministry added.
Russia's aviation industry remains blighted by repeated accidents involving its ageing fleet of planes and helicopters.
Poor maintenance and lax safety precautions are also often blamed for frequent accidents