Manzoor Hussain of the Pakistan Alpine Club said two surviving members of the Spanish expedition, which was trying to summit Gasherbrum I in the Karakorum range near the Chinese border, have informed Pakistan officials that their missing comrades are "dead by now".
They were part of a five-member team and lost contact with their colleagues on Monday while descending the peak.
"After losing contact with them on the morning of July 22 and given the adverse conditions at (high) altitude in the following days, we made one more flight search that confirmed our worst fears: the three have died," the surviving climbers said in a statement issued to Spanish media.
Last week, Pakistan authorities abandoned the search for three Iranian climbers who went missing while trying to summit Broad Peak in the same region.
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Officials said the Iranians too are "presumed dead".
The year has been particularly hard for foreign climbers in Pakistan.
Last month, 10 of them were killed by militants in the base camp of Nanga Parbat.
A German woman trekker also died two weeks ago.