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The families of two U.S. mountain climbers missing for almost two weeks in Pakistan ended the search and rescue effort late Saturday.

Kyle Dempster, 33, and Scott Adamson, 34, well-known alpinists from Utah, were ascending a mountain peak known as Ogre II on Aug. 21 and were supposed to return to their base three days later, said Black Diamond Equipment, an outdoor company sponsoring Dempster.

They were trying to scale the 23,901-foot mountain's North Face, the company said.

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Kyle Dempster (left) and Scott Adamson. GoFundMe

"Given the time that has elapsed and the nearly continuous stormy weather since they were last seen, and the substantial risks that such high-altitude missions entail, Kyle and Scott's families have made the extremely difficult decision to end the search efforts," Black Diamond said in a statement.

Global Rescue, a travel risk and crisis management firm involved in the search, said a Pakistan military helicopter conducted flights over the the climbers' likely locations Saturday. A second helicopter was dispatched after the first one had to refuel, but there were no immediate signs of the men.

"In light of those extensive yet unsuccessful efforts, the search team and knowledgeable observers in Pakistan, the US, and Europe, assessed that there remained a very slim chance that any evidence of their passage would be revealed in subsequent sweeps of the mountain," Black Diamond said.

Related: Utah Climbers Go Missing on Pakistan Peak

The last confirmed sighting was of the men's headlamps on Aug. 22 by a Pakistani member of their base camp team. Neither climber was believed to be carrying satellite communication or messaging capabilities, Global Rescue added.

This was not their first time climbing this particular peak in Pakistan.

Adamson broke his ankle near the summit after tumbling 100 feet, and the pair also fell 400 feet as they tried to get off the mountain last year, but they were unharmed, friends said.