The aircraft was reported missing with four Marines on board Friday evening, shortly after it had been scheduled to land in the northern Norwegian city of Bodø. Nordland Police Chief Bent Arne Eilertsen told Verdens Gang that there was no indication of survivors as ground crews approached the area of the crash.

The Osprey is a hybrid aircraft that lands and takes off vertically. American officials have confirmed the crash, while offering few other details.

“We can confirm an incident has occurred involving a Marine Corps MV-22B Osprey aircraft,” Major Jim Stenger, U.S. Marine Corps spokesperson, said in a statement obtained by Newsweek. “The aircraft was conducting training in Norway as part of Exercise COLD RESPONSE 22 at the time of the incident.”

“The cause of the incident is under investigation,” Stenger added. “Additional details will be provided as available.”

According to the Norwegian Armed Forces, the aircraft’s last known position was in the mountainous region of Saltfjellet, south of its landing site in Bodø.

A rescue helicopter mission was canceled after weather conditions in the area made an air approach to the crash site impossible, forcing rescue crews to travel on snowmobiles and by foot. Conditions were expected to get worse through the night.

A statement released by the II Marine Expeditionary Force noted that “Norwegian civil authorities are leading the search and rescue efforts at this time” and that the U.S. would provide assistance “in all manners possible.”

Earlier this month, a NATO press release described Cold Response 2022 as “a long-planned exercise bringing together thousands of troops from NATO Allies and partners, testing their ability to work together in cold weather conditions across Norway—on land, in the air and at sea.”

NATO noted that the exercise had been announced over eight months earlier and was “not linked to Russia’s unprovoked and unjustified invasion of Ukraine,” although it was planned to ensure “that our armed forces are prepared to respond to any threat or crisis.”

However, NATO forces have been in a state of heightened alert while conducting training exercises in European member countries amid the war in Ukraine, with U.S. troops playing a key role.

While Norway is a NATO member, its nordic neighbors Sweden and Finland, which like Norway directly borders Russia, are not members despite often cooperating with the alliance.

Last week, a spokesperson from Russia’s Ministry of Foreign Affairs warned that Norway’s neighbors would face “serious military and political consequences” if they became members. The ministry issued a similar warning as the Ukraine invasion first began.

The Cold Response 2022 exercise began on Monday and is expected to continue into April. It is unclear what impact the Osprey crash might have on the exercise, which includes the participation of around 3,000 U.S. Marines out of around 30,000 NATO troops in total.