American mountain climbers Kyle Dempster and Scott Adamson earned reputations as two of the world's best by setting out to conquer icy, steep routes others couldn't scale.

That fearlessness led them to a treacherous mountain peak in a remote part of Pakistan for their second attempt at making a climb never done before. They nearly died last year on their first try, miraculously surviving a 400-foot fall.

This time, they did not make it off the mountain.

A search launched Aug. 28 was called off Saturday by their families after helicopters found no signs of the men or their equipment.

On Tuesday, search officials acknowledged Dempster and Adamson are presumed dead.

They went missing in stormy conditions on the north face of a 23,901-foot peak known as Ogre II.