OSLO (Reuters) -All four people on board a U.S. military aircraft were killed when it crashed in a remote part of northern Norway on Friday during a NATO-led military training exercise, local police said on Saturday.

       "As far as the police are aware, all four are of American nationality," police said. Prime Minister Jonas Gahr Stoere tweeted condolences over what he said was the death of four Americans.

       The MV-22B Osprey aircraft belonging to the U.S. Marine Corps was taking part in an exercise called Cold Response.

       Rescue services reached the crash site by land early on Saturday after helicopters were unable to land due to poor weather conditions. Gale-force winds were blowing, heavy rains were falling, and there was a risk of avalanches, 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.

       Police were investigating the cause of the crash although their work was halted because of the weather conditions. The work was set to resume once the weather improves.

       Some 30,000 troops from 27 countries are involved in Cold Response, an exercise designed to prepare NATO member countries for the defence of Norway.

       (Reporting by Terje Solsvik and Gwladys FoucheEditing by Frances Kerry)