COPENHAGEN — Four American soldiers were killed in a plane crash during a NATO exercise unrelated to the Ukraine war, Norway’s prime minister said Saturday.

Jonas Gahr Støre tweeted that they were killed in the crash on Friday night. The cause was under investigation.

The Norwegian Armed Forces confirmed on Saturday the death of the four soldiers.

"The police in Nordland County now confirm that the crew of four have died. As far as the police know, the four are of American nationality," said a press release from the Norwegian Armed Forces.

"Apart from the crew, there were no other people on board the Osprey," it said, referring to the aircraft Bell-Boeing V-22 Osprey which crashed on a training mission in the ongoing North Atlantic Treaty Organization (NATO) exercise dubbed "Cold Response" scheduled from March 10 to April 10.

The circumstances of the accident have yet to be clarified. According to the Norwegian Armed Forces, the Cold Response exercise will go on as planned.

"It has now sadly been confirmed that the crew on board the American aircraft died in the accident," said Norwegian Chief of Defense Eirik Kristoffersen in the press release.

Cold Response, dubbed the largest Norwegian-led military exercise since the Cold War, involves 30,000 military personnel, 220 aircraft, and over 50 vessels from NATO countries. — Agencies