Four US marines were killed when their Osprey aircraft crashed in a Norwegian town in the Arctic Circle during a Nato exercise unrelated to the Ukraine war, authorities said on Saturday. The Norwegian prime minister, Jonas Gahr Stoere, tweeted that the marines died on Friday night. The cause was under investigation but Norwegian police reported bad weather. The marines, assigned to 2nd Marine Aircraft Wing, II Marine Expeditionary Force, were taking part in a Nato exercise called Cold Response. The US said the identities of the marines wouldn’t be immediately provided in keeping with defense department policy of notifying relatives first. The aircraft was an MV-22B Osprey with “a crew of four [which] was out on a training mission in Nordland county” in northern Norway, the Norwegian armed forces said. It was on its way north to Bodoe, where it was scheduled to land just before 6pm. The Osprey crashed in Graetaedalen in Beiarn, south of Bodoe. Police said a search and rescue mission was launched immediately. At 1.30am on Saturday, police arrived at the scene and confirmed that the crew of four had died. The annual Nato drills in Norway are unrelated to the war in Ukraine. This year they include about 30,000 troops, 220 aircraft and 50 vessels from 27 countries. Non-Nato members Finland and Sweden are also participating. The exercises began on 14 March and end on 1 April. The Norwegian armed forces said Cold Response “will carry on as planned, with the measures we have to take due to the weather”. A Norwegian rescue helicopter spotted the crash site late on Friday and local Red Cross crews were assigned to assist police on the ground, Norwegian media said. The Norwegian newspaper VG said Red Cross members drove close to the crash site with scooters and marked the trail with GPS for police in what they described as extremely difficult weather conditions. “It was a special night, it was a real storm. There were five of us driving towards the scene of the accident. There was one meter of visibility, snow and storm in the mountains,” Red Cross team leader Oerjan Kristensen told VG. “I guess it was a wind gust of 30-40 meters per second. When it blows like that, it is difficult to stand upright.” Kristensen added that the rescue operation was hampered by the risk of landslides in the mountains and the remoteness of the crash site. Police launched an investigation and accident commission members and police representatives were due to arrive at the crash site on Saturday. “The weather is very bad in the area to complete work at the scene but police will take it up again as soon as the weather conditions allow it,” operations manager Ivar Bo Nilsson from the Norland police district told reporters. Lt Gen Yngve Odlo, head of the Norwegian armed forces’ operational headquarters, said Cold Response would continue. “Right now there is full focus on ending the rescue operation, taking care of the people and then there will be a normal procedure with causation,” Odlo was quoted as saying by Norwegian public broadcaster NRK. The first Cold Response was held in 2006, and the drills have been conducted eight times. They take place in south-eastern, central and northern Norway.