Eighteen people have died in a Russian helicopter crash in north-western Siberia, officials say.
"According to preliminary information, the blades of the helicopter collided with cargo on the external load sling system of the Mil Mi-8AMT, RA-22427, which had taken off earlier".
"There were three crewmembers and 15 passenger overseas the Mi-8 that belonged to Utair airline", he said.
The oil field is operated by Russian national oil company Rosneft through its subsidiary Vankorneft.
The investigators are checking the flight documentation, taking fuel samples and interrogating maintenance personnel, employees of the airline and witnesses of the crash, the committee said. A UTair ATR 72 crashed in Siberia in 2012, killing 33 of the 43 people aboard, after failing to be de-iced before takeoff.
The two aircraft were owned by UTair-Helicopter Services, a unit of Russian airline UTair.
The crew of the cargo-carrying helicopter were not injured and there was no adverse weather conditions, said Rosaviatsia.
The helicopter was manufactured in 2010.
The country's Investigative Committee said it opened a criminal investigation into the crash.
Law enforcers said that all possible versions were under consideration, including a crew error and equipment failure.