Fifteen people were killed in Russia on Thursday when a civilian helicopter crashed in Siberia, regional authorities said.The Mi-8 helicopter, which was transporting 22 passengers and four crew members, crashed outside the town of Igarka in Western Siberia, some 2,800 kilometres (1,750 miles) northeast of Moscow."Fifteen people were killed and 10 people were hospitalised as a result of the crash," regional transportation authorities said in a statement.Most of the 26 people on board were oilfield workers. Ten people were taken to hospital and were in intensive care, TASS news agency said. Other news reports had slightly different numbers of occupants and casualies.Contact with the helicopter -- which was headed to an oil pumping station -- was lost just after 0400 GMT, some 15 minutes after takeoff from Igarka airport, authorities said.The regional branch of the emergencies ministry said the helicopter had performed an emergency landing but did not elaborate on what might have caused the crash.Two helicopters were sent to the area for rescue operations.Authorities suspected a technical fault to be the cause of the crash, but have not excluded pilot error.Prosecutors said they would investigate possible safety violations.