Kyle Dempster Scott Adamson
The search has been called off for US climbers and long-time friends Kyle Dempster (l) and Scott Adamson (r).GoFundMe

The search has been called off for two missing US climbers attempting to summit Pakistan's highest peak after a rescue team failed to find any sign of them. Utah climbers Kyle Dempster, 33, and Scott Adamson, 34, were attempting to summit the treacherous north face of the 22,835-feet (6,960m) Ogre 2 peak in the Karakoram mountain range.

Rescuers in two helicopters spotted no sign of the men nor any camps, said search spokesman Karrar Haidri.

"It seems that a big avalanche had occurred," Haidri told Reuters.

Family spokesman Jonathan Thesenga told CNN that the search had been terminated and friends and relatives did not want to risk anymore lives.

"The search has been called off," Thesenga said. "It was an extremely difficult time for the friends and family waiting and hoping for good news. And it's been devastating to come to the decision to call off the search."

He said loved ones had remained optimistic that the men would be found, and are trying to come to terms with the fact that they are not coming home.

"There were a couple of deciding factors in calling off the search, one was the time they had been gone — the very small amount of hope we had was gone," he said.

"When the extensive search did not yield any visible signs, they made the decision that it would not be wise to risk (this) dangerous search mission with helicopters."

Both men were experienced climbers. Dempster had won the prestigious Piolet d'Or alpine climbing award twice. They set off on the trek 21 August, and expected the climb and descent would take five days. A major storm hit the mountain the following day.

The two friends had tried to summit the treacherous north face of Ogre 2 last year — but turned back after Adamson broke his leg in a fall. Ogre 2 is one of the steepest peaks in the region. The climbers were attempting a route up the north face never done before.

In a recent video Dempster said: "On that journey, you go through the feeling of fear and to an eventual outcome. You use your pool of experience and common sense and intuition to help make decisions and mitigate the dangers."

The family had raised nearly $200,000 for the search on Go Fund Me. They thanked the Pakistani government for "scrambling all of their available assets and their commitment to finding Scott and Kyle."