MONTREAL • Three world-renown-ed professional mountaineers - two Austrians and an American - were missing and presumed dead after an avalanche on a western Canadian summit, the country's national parks agency has said.

American Jess Roskelley, 36, and Austrians Hansjorg Auer, 35, and David Lama, 28, went missing on Tuesday evening in Banff National Park, according to media reports. The authorities launched an aerial search the next day.

The three men were attempting to climb the east face of Howse Pass, an isolated and highly difficult route, Parks Canada said on Thursday.

They were part of a team of experienced athletes sponsored by American outdoor equipment firm The North Face, the company confirmed to Agence France-Presse.

Rescuers found signs of several avalanches and debris consistent with climbing equipment, Parks Canada said, leading them to presume that the climbers were dead.

Poor weather conditions have increased avalanche risks in the mountainous area on the border between Alberta and British Columbia, with the search halted for safety reasons.

It is unlikely the three men survived, Mr John Roskelley, father of missing mountaineer Jess Roskelley, told local media in the US state of Washington. "This route they were trying to do was first done in 2000. It's just one of those routes where you have to have the right conditions or it turns into a nightmare. This is one of those trips where it turned into a nightmare," he told the Spokesman-Review.

Himself considered one of the best American mountaineers of his generation, Mr John Roskelley climbed Mount Everest with his son in 2003, making then 20-year-old Jess the youngest person to have conquered the summit.

AGENCE FRANCE-PRESSE