All four U.S. personnel aboard a military aircraft were killed when the plane crashed in a remote part of northern Norway on Friday during a NATO training exercise, the Norwegian armed forces said in a statement on Saturday.

The V-22B Osprey aircraft belonging to the U.S. Marine Corps was taking part in Cold Response, a long-planned military exercise to practice defending Norwegian territory in cold-weather conditions in case of attack.

Rescue services reached the crash site by land early on Saturday after helicopters were unable to land due to poor weather conditions, including gale-force winds and heavy rain.

There was also a risk of avalanches in the area, according to local weather forecasts.

"Police reached the crash site at around 0130 CET (0030 GMT). It is regrettably confirmed that all four on board the plane have perished," Ivar Bo Nilsson, head of the operation for Nordland police, said in a statement.

A Norwegian armed forces statement said later the four who had died were the Osprey's "American crew".

Police investigating the cause of the crash had to halt their work because of the bad weather, planning to resume their probe when the conditions improved.

Some 30,000 troops from 27 countries are involved in Cold Response, which Norway's military said would continue.