The last search helicopter was withdrawn shortly after midnight from the area around Mount Kebnekaise, Sweden’s highest peak, amid severe weather conditions and very poor visibility.

The area was officially designated an accident zone on Friday evening after rescue teams found pieces of metal wreckage on both sides of the mountain in the far north of Sweden, some 150 kilometres above the Arctic Circle.

Swedish rescue workers leading the search operation said the airplane itself had not yet been found.

A Swedish unit at Storglaciären (‘The Grand Glacier’) confirmed it had found a padded object and a Velcro strip, both of which were soaked with paraffin.

Norway’s defence minister, Espen Barth Eide, admitted he now feared the worst.

”I want to underline that we don’t know what happened, but there are more and more indications of a very serious accident, with wreckage spread out over a large area,” he told Norwegian broadcaster NRK.

The aircraft went missing on Thursday afternoon when it was on its way from Evenes in northern Norway to Kiruna in the far north of Sweden.

At the time, the Hercules was participating in the Cold Response military training exercise taking place over northern Norway which was scheduled to run from March 12th to March 21st and included 16,000 soldiers from 15 countries.

"There was a crew of four on board as well as an extra officer. Their mission was to fly from Evenes to Kiruna to pick up materiel and personnel and fly back to Norway," Harald Sunde, head of the Norwegian Armed Forces told Norwegian news agency NTB.

He added that the officers on board the Hercules aircraft were among the "most experienced" in the Norwegian military and that there were no clues regarding what may have happened.

"We have nothing that points us in any particular direction. This is a very robust and new aircraft, one of the best there is. It's been hard to have bad luck with this type of aircraft," said Sunde.

The missing aircraft is a C-130 J "Super" Hercules transport plane manufactured by Lockheed Martin in the United States.

The plane is one of four C-130 Js ordered by the Norwegian air force in 2007, the first of which was delivered in November 2008.