Nepalese volunteers and friends carry the body of Ueli Steck at a hospital in Kathmandu. (Prakash Mathema/AFP/Getty Images

A famed mountain climber known as the “Swiss Machine” was killed under circumstances that are still unclear in a mountaineering accident near Mount Everest in Nepal.

Ueli Steck, who emphasized the athletic aspect of climbing over the adventure, is the first casualty in the spring mountaineering season that draws hundreds of climbers and runs from March until May. Steck was planning to climb 29,035-foot Mount Everest and nearby Mount Lhotse in the coming weeks. According to the BBC, he died as he was acclimatizing for an attempt to climb Everest, taking a new route to the summit without oxygen.

Steck, who was known for rapid ascents and had scaled dozens of Alps peaks in just over two months, was killed at Camp 1 of Mount Nuptse, Mingma Sherpa of Seven Summit Treks told the Associated Press. His body was taken to the only airport in the Mount Everest area, in Lukla.

“The family is infinitely sad and asks that the media refrain from speculating about his death out of respect and consideration for Ueli,” a statement on Steck’s website said. “As soon as reliable information about Ueli Steck’s death becomes available, the media will be informed.”

Steck had been seen climbing near the Nuptse Face just west of Everest early Saturday and the Himalayan Times wrote that he may have slipped and fallen on the icy slope.

Last week, he had written on Facebook that he had “a quick day from Basecamp up to 7,000 [meters] and back” as he pursued “active acclimatization.”

Quick Day from Basecamp up to 7000m and back. I love it its such a great place here. I still believe in active aclimatisation. This is way more effective then spending Nights up in the Altitude!

Posted by Ueli Steck on Wednesday, April 26, 2017

Steck, 40, summited at Everest without oxygen in 2012 and spoke in a in a video recently about the difficulty of climbing Everest and Lhotse via the Hornbein Couloir.

“Why do I have to attempt Everest and Lhotse? Yet again, the answer is simple: I get to stay longer in the mountains,” he said in the video. “And now I’ll just go, and only worry about the events that lie ahead of me. Day by day, one by one. It is the here and now that counts. What comes next is uncertain in any case.

“Learn from yesterday, live for today, hope for tomorrow.”

Steck set several records for ascending the north face of the Eiger, a classic mountaineering peak in the Bernese Alps that he climbed in 2 hours 47 minutes without using a rope. Two years ago, he climbed all of the Alps peaks higher than 13,100 feet in 62 days, hiking, biking and paragliding between peaks. The feat only solidified his “Swiss Machine” nickname.

Four years ago, he successfully completed the first solo climb of the Annapurna south face, where he nearly died in a fall in 2007.