Alexei Leonov, the legendary Soviet cosmonaut who became the first human to walk in space 54 years ago, has died in Moscow at 85.

The Russian space agency Roscosmos announced the news on its website on Friday, but gave no cause of death. Leonov had health issues for several years, according to Russia media.

Showing just how much of a space pioneer Leonov was, Nasa interrupted its live televised coverage of a spacewalk by two Americans outside the International Space Station to report Leonov’s death.

“A tribute to Leonov as today is a spacewalk,” Mission Control in Houston said.

Leonov was an icon both in his country as well as in the US, so much so that the late science fiction writer Arthur C Clarke named a Soviet spaceship after him in his 2010 sequel to 2001: A Space Odyssey.

The Russian president, Vladimir Putin,sent his condolences to Leonov’s family, calling him a “true pioneer, a strong and heroic person”.

Leonov staked his place in space history on 18 March 1965, when he exited his Voskhod 2 space capsule secured by a tether.

“I stepped into that void and I didn’t fall in,” the cosmonaut recalled years later. “I was mesmerised by the stars. They were everywhere – up above, down below, to the left, to the right. I can still hear my breath and my heartbeat in that silence.”

Spacewalking always carries a high risk but Leonov’s pioneering venture was particularly nerve-racking, according to details of the exploit which only became public decades later.

His spacesuit had inflated so much in the vacuum of space that he could not get back into the spacecraft. He had to open a valve to vent oxygen from his suit to be able to fit through the hatch.

Leonov’s 12-minute spacewalk preceded the first US spacewalk, by Ed White, by less than three months.