Mohammed Hassan, 27, slipped and fell off a narrow trail in a particularly dangerous area of K2, the world's second-highest peak, known as the bottleneck.

Renowned Norwegian mountaineer Kristin Harila has denied claims her team stepped over a dying Mr Hassan as part of a world record bid last month after video emerged showing climbers appearing to step over the high porter.

Basharat Hussain, a childhood friend of Mr Hassan, described it as "the most dehumanising event of [his] life".

He said: "The climbers, who scaled the K2 this year, I understand their behaviour was below humanity and it was very saddening, after they walked past the man after he was gravely injured in a fall and they scaled the K2.

"I think this is the most dehumanising event in my life. It may have not happened in the past, it has not happened in the present, and I hope it will not happen in the future."

An investigation has been launched into the claims that climbers left Mr Hassan to die near the peak of the world's most treacherous mountain.

Harila, 37, has rejected any responsibility for the death of the father of three and said she is the victim of "misinformation" and has had "hatred" aimed at her - including death threats.

Last month, she became the fastest climber to scale all the world's 14 highest mountains - completing the achievement in just 92 days.

Her final climb was of K2 on 27 July, after which she arrived with fellow record-breaker, Nepali mountaineer Tenjen (Lama) Sherpa, in Kathmandu to a hero's welcome.

But during the K2 climb, a local helper who was part of a team ahead of them, slipped a few metres from a narrow ledge, became tangled in ropes and later died on the mountain.

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Harila has defended herself against allegations from two other climbers who were on K2 that day, Austrian Wilhelm Steindl and German Philip Flaemig.

The pair had aborted their climb because of difficult weather conditions, but said they reconstructed the events later by reviewing drone footage.

The investigation is being conducted by officials in the Gilgit-Baltistan region which has jurisdiction over K2, said Karrar Haidri, the secretary of the Pakistan Alpine Club, a sports organisation that also serves as the governing body for mountaineering in Pakistan.