Sherpas in Nepal have found four more people dead in their tents on Mount Everest, officials announced Wednesday. Authorities say they believe the four climbers died of carbon-monoxide poisoning, which raises the death toll on the mountain to 10 in the last four weeks. The climbers’ identities have not yet been established, said Mingma Sherpa, of the Seven Summit Treks group, in Kathmandu. The climbers were at Camp Four, which is at 24,246 feet. Himalayan Times reported that at least two of the climbers who died overnight on the world’s largest mountain were foreigners. Rescuers said they believed they had suffocated. The sherpas found the bodies on their way to retrieve another dead climber, Slovakian Vladimir Strba, who died near the 29,035-foot summit over the weekend. At least 5,000 climbers have successfully scaled Mount Everest since 1953, and as many as 300 others have died in the attempt.