Norway’s prime minister said Saturday that four U.S soldiers lost their lives in a plane accident during a NATO exercise that had nothing to do with the Ukraine conflict.

On Friday night, Jonas Gahr Støre stated on twitter that they had been killed in the incident and the inquiry was ongoing.

“The soldiers participated in the NATO exercise Cold Response,” he said. “Our deepest sympathies go to the soldiers’ families, relatives and fellow soldiers in their unit.”

According to Norway’s military, the aircraft was a US Marine Corps V-22B Osprey.

“The aircraft had a crew of four and was out on a training mission in Nordland County” in northern Norway, as per the statement.

After departing from Oslo, the plane was due to arrive in the Norwegian city of Bodø shortly before 6 p.m Friday. A search and rescue effort was immediately initiated, according to authorities. The police arrived at the site at 1:30 a.m. on Saturday and established that the four crew members had died.

No connection can be made between the regular NATO exercises in Norway and the ongoing conflict in the Ukraine. Around 30,000 soldiers, 220 planes, and 50 ships from 27 nations took part in this year’s exercise. Finland and Sweden, who are not members of NATO, are also participating.

Starting on March 14, the workouts will go through the end of April 1.

The Cold Response “will carry on as planned, with the measures we have to take due to the weather”, the Norwegian armed forces announced after the accident.