Four U.S. Marines were killed on Friday when an American MV-22 Osprey aircraft crashed during a large NATO military exercise in Norway, the Norwegian prime minister said.

“It is with great sadness we have received the message that four American soldiers died in a plane crash last night,” Prime Minister Jonas Gahr Støre said on Saturday on Twitter. “The soldiers participated in the NATO exercise Cold Response. Our deepest sympathies go to the soldiers’ families, relatives and fellow soldiers in their unit.”

Search and rescue teams had been looking on Friday for the missing aircraft in northern Norway.

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

Stenger said the incident remains under investigation.

The Second Marine Expeditionary Force later issued a statement confirming it was aware of “a mishap” with an Osprey assigned to its command.

Currently there are 3,000 U.S. Marines in northern Norway participating in the Cold Response 22 NATO exercise that is described as one of the largest NATO exercises since the end of the Cold War. There are 30,000 troops total participating in this year’s exercise.

Held every two years, the exercise was planned long before the Russian invasion of Ukraine and helps to train multinational NATO forces in how to operate in the Arctic.

Norway’s Armed Forces and the Joint Rescue Coordination Centre of Northern Norway issued statements Friday confirming they were conducting a search for a missing Osprey aircraft that had failed to land at its destination.

“The Osprey belongs to the U.S. Marine Corps and is taking part in the Norwegian military exercise Cold Response in Norway,” said the statement from Forsvaret, Norway’s armed forces. “The aircraft has a crew of four and was out on a training mission in Nordland County, northern Norway on Friday 18 March 2022.”

The statement said the Osprey was en route to Bodø, where it was scheduled to land just before 6 p.m. local time and was reported missing at 6:26 p.m. local time with its last known position being south of Bodø.

Search and rescue aircraft were launched but weather conditions in the area are described as “challenging and are expected to get worse.” An apparent crash site south of Bodø was located from the air three hours later.

“Due to the weather conditions, it has not been possible to enter the site from the air,” said the Norwegian armed forces statement. “Police and rescue crews are now on their way into the area.”

This is a developing story. Check back for updates.