Elite Exped said Nepali mountaineer Nirmal Purja and nine other members of his team died in an avalanche on Broad Peak in Pakistan's Skardu region.
The group went missing on 30 July while climbing the mountain.
The expedition operator confirmed the deaths on 1 August.
The avalanche struck at an elevation of about 6,600 metres, the account said.
Tracking-device data indicated that the climbers were thrown hundreds of metres down the mountain slope.
Purja, 42, previously set a record for climbing all 14 of the world's highest mountains in the shortest time.
Before the accident, he had said he was close to completing a second ascent of all 14 peaks without supplemental oxygen.
Broad Peak is in the Karakoram range and is widely regarded as a difficult, high-risk mountain.