More than 50 people were reported to have died after smoke filled a Siberian coal mine and a rescue effort ended in tragedy.
Senior managers at the mine in Russia's Kemerovo region had been detained for suspected safety violations, after the latest deadly accident to hit the country's vast mining industry.
Russian news agencies quoted local authorities as saying that 52 people were dead, including miners and six rescuers who had been part of an aborted search operation.
"According to preliminary information, no one is left alive in the mine," state news agency TASS quoted a source in the local emergency services as saying.
The Listvyazhnaya mine, near the town of Belovo in the Kemerovo mining region, filled with smoke in the early hours of today with 285 people inside.
Most were able to evacuate, but officials had said 35 miners were unaccounted for.
It was not immediately clear what had caused the accident, though some Russian media reported that dust in a ventilation shaft caught fire, causing the mine to fill with smoke.
News agency RIA Novosti quoted prosecutors as saying a spark may have set off a methane explosion.
A search and rescue operation was launched but called off several hours later after officials warned of the threat of an explosion.
There were reports of rescuers running low on oxygen and news agencies said the bodies of six of them were found.
Private news agency Interfax quoted a local official as saying they had suffocated.
Russia's Investigative Committee, which probes major cases, opened a criminal probe and said three people had been detained including the 47-year-old director of the mine and his 59-year-old first deputy.
"During the initial investigation, it was established that the detainees violated industrial safety requirements," the committee said in a statement.
Nearly 40 people were hospitalised, regional authorities said. The governor declared a three-day mourning period in the region.
Earlier in the day residents of the village of Gramoteino next to the mine gathered in snowfall and sub-zero temperatures outside the entrance to the facility, which was closed off with a boom gate, as ambulances passed in and out.
There was no panic but the crowd was tense and refused to speak to journalists.
"This is a great tragedy," Russian President Vladimir Putin said during talks with Serbian leader Aleksandar Vucic in Sochi.
"Unfortunately, the situation is not getting any easier. And even rescuers are in danger."
Local investigators said smoke spread across the mine at around 8:35am local time and that "a number of workers suffered smoke poisoning".
The Investigative Committee, which probes major cases, opened a criminal probe into the possible violation of safety regulations that led to deaths.