Image copyright European photopress agency Image caption Dean Potter and his dog Whisper

Dean Potter - one of America's best known extreme athletes - has been killed during a stunt in California.

The 43-year-old died while attempting a wingsuit flight from the 7,500 ft (2,286m) Taft Point promontory in Yosemite National Park, a park spokesman said.

Fellow extreme athlete Graham Hunt also died as the pair attempted to fly at high speed.

Rescuers found the bodies soon after contact had been lost with the men.

The men were wearing skin tight suits with batwing sleeves and a flap between their legs to help them glide.

Park ranger Scott Gediman said that their parachutes had not been deployed.

"This is a horrible incident, and our deepest sympathies go out to their friends and family," Mr Gediman told the AP news agency. "This is a huge loss for all of us."

Such stunts are illegal in the National Park but enthusiasts frequently manage to evade the authorities.

Dean Potter: The sensation of high-line walking

My vision turns black and white except for the searing red line.

Sounds fade. I feel faint, face flushed with heat.

My muscles tense, but I hold calmness in my centre and loosen my arms from the shoulders to my fingertips.

The moment sickens me, and my mind tries to stop it, but I command myself to walk.

From deanspotter.com

Base jumping: 'It's an addiction'

Image copyright Rex Features Image caption Potter frequently wingsuit jumped in Yosemite National Park

Image copyright Shawn Reeder Image caption Graham Hunt died alongside Potter - the two were frequent climbing companions

Image copyright AP Image caption Potter was renowned for his high-line walking

The world of extreme sport has paid tribute to Potter, a climber who continuously pushed the limits of what was possible.

He was a leading practitioner of "extreme highlining": walking across a tightrope between rock formations with only a parachute for safety.

Those who worked with him say that base jumping - basically jumping from a fixed structure like a building or cliff - was possibly his greatest risk.

"Base jumping is the most dangerous thing you can do... every time you jump it's a roll of the dice," photographer Corey Rich told the AP news agency.

"The odds are not in your favour, and sadly Dean pulled the unlucky card."

Last year the nutrition company Clif Bar withdrew their sponsorship of Potter and four other top climbers, as it felt uncomfortable with the risks that they were taking.

Image copyright AP Image caption Potter was one of the most innovative rock climbers in the history of the sport

Media playback is unsupported on your device Media caption Climber Doug Robinson: ''He knew that he was out on the edge and taking risks''

Potter was the first to climb Yosemite's three most famous big walls in a single day. Earlier this month he set a record for the fastest ascent of one the park's most well known rock formations, the Half Dome,

He was also renowned for his high-line walks and high-risk parachute jumps, some of which he carried out with his dog, Whisper.

Last year he released a 22-minute long film, When Dogs Fly that chronicled Whisper's extreme adventures. Although it became a viral sensation, it also attracted criticism from animal rights activists.

Climber Doug Robinson told the BBC that Potter had always sought to take on new challenges.

"We're very sad about Dean Potter's death, but not very surprised," he told BBC Newsday, "he was pushing the envelope all his life."