MOTÖRHEAD ended their concert in Salt Lake City, Utah, after four songs last night (August 27th) as frontman Lemmy told the crowd he was finding it difficult to breathe, reported classicrockteamrock.com.

It follows reports from Los Angeles on August 22nd, where some fans said the 69-year-old appeared unsteady on his feet.

The rock icon has been in frail health since undergoing heart bypass surgery and later suffering a haematoma in 2013.

MOTÖRHEAD moved to reassure supporters that the problem was caused by the city’s altitude. They said via their official Facebook page: “The people are great, but the air is just too thin. The high altitude makes it difficult for breathing, and that’s what happened with Lemmy tonight in Salt Lake City.

“He feels very bad to have cut the show short, but being that high up, he had some trouble breathing well. Lemmy appreciates everyone’s concern. The fans always rally round!”

But the explanation raises the prospect of further cancellations. Salt Lake City is 4200ft above sea level, while Denver, Colorado, where the band are due to play tonight, is 5300ft above sea level.

MOTÖRHEAD’s 22nd album “Bad Magic” is released today. They’re scheduled to end a UK tour with a special 40th anniversary concert at London’s Eventim Apollo on January 29.

WEST HOLLYWOOD, CA – JANUARY 17: 57th Annual GRAMMY Awards nominee Lemmy Kilmister of Motorhead attends Los Angeles GRAMMY Nominee Celebration – LA Chapter on January 17, 2015 in West Hollywood, California. (Photo by Rebecca Sapp/WireImage for NARAS)