Six soldiers on an alpine training exercise on Switzerland's Jungfrau mountain were killed Thursday when an avalanche sent them plummeting thousands of feet into a valley, the army said.

The soldiers, who were taking part in mountaineering training in the popular Bernese Alps, were from a 14-member patrol that was scaling Jungfrau, about 55 miles southeast of the capital of Bern, said Fred Heer, the army's deputy commander.

The other eight soldiers were rescued by helicopter and were unharmed, he said.

The victims were from the country's French-speaking region, Heer said. The army launched an investigation into the incident — the worst of its kind in Switzerland since 12 people died in an avalanche in 1999.

Rescue officials said the victims were ascending the southern face of the 13,642-foot mountain in two teams of three when the accident occurred.

Rene Feuz of the rescue station in nearby Lauterbrunnen told The Associated Press the soldiers had reached a height of 12,470 feet when fresh snow dislodged, causing them to fall more than 3,000 feet into the valley below.

All six bodies were recovered, he said.

All able-bodied Swiss men must perform military service, which lasts about 10 months and frequently includes specialist training in rugged terrain.