Soviet cosmonaut Valery Kubasov, who took part in the first docking of a US Apollo spacecraft with a Soviet Soyuz, has died aged 79, the Russian spacecraft corporation said Thursday.

Kubasov was one of two crewmembers of the Soyuz 19 spacecraft that docked with the US Apollo spacecraft on July 17, 1975, marking both a technical breakthrough and a rare relaxation in Cold War tensions.

He died suddenly on Wednesday after a short illness, the Russian space corporation RKK Energiya said in a statement on its website.

The historic docking saw Soyuz commander Alexei Leonov shake hands with American astronaut Thomas Stafford, a gesture that was watched on television around the world.

Leonov said that when the US astronauts crossed into the hatch, they saw an inscription from Shakespeare: "Brave new world that has such people in it."

The teams then worked together for two days.

Four original crewmembers including Kubasov, who was the flight engineer, met in Moscow in 2010 to mark the 35th anniversary of the docking.

Kubasov recalled that the US crewmembers had surprised the Soviet cosmonauts by connecting them by radio with US President Gerald Ford who spoke to both of them, Rossiiskaya Gazeta daily reported.

The docking of the two crafts tested out pioneering technology that paved the way for the International Space Station.

Kubasov was twice decorated as a Hero of the Soviet Union, the country's top honour.

After training at Moscow's aviation institute, he began working as an engineer involved in spaceship construction before becoming a cosmonaut in 1966.

On his first space flight in 1969, he was the first ever to experiment with welding in open space. The Soyuz mission was his second space flight.

His third and last space flight was a 1980 mission to a Soviet orbital space station, Salyut 6.

Kubasov was a "strong personality, a man out of the ordinary," said the RKK Energiya statement.

He was a "brave instructor, cosmonaut and test pilot who made a significant contribution to studying space and learning the secrets of the Universe."