A Russian Mil Mi-8 helicopter crashed in the Democratic Republic of Congo and the fate of the crew is unknown, RIA Novosti reported citing a source in Russia’s law-enforcement agency.

The helicopter, which belonged to Russian airline UTair, worked in the central African country under a UN contract.

“According to preliminary information, a Russian Mi-8 helicopter crashed in the mountainous terrain at an altitude of 2,700 meters, some 20 km [12 miles] south-west of the town of Bukavu,” the source said.

There were four crew members, all of them Russian nationals, aboard the helicopter.

UTair has earlier reported a Mi-8AMT helicopter was performing a Shabunda-Bukavu flight on Saturday in complex weather conditions. Communication with the helicopter interrupted some 10 miles from the Bukavu airport.

The helicopter was detected in hard-to-access terrain on Sunday, March 10 at an altitude of 2,700 meters.