The event marks the end of an era for American-Russian space co-operation. It is the last visit by the US shuttle to the ageing Russian space outpost.

But as one chapter ends, another begins with Russians and Americans set to work together to create an international space station.

Discovery was linked to Mir for four days

"We have physical separation," Discovery pilot Dom Gorie reported as he fired rocket thrusters at 1601 GMT to pull away from the sprawling space complex, orbiting 239 miles above Earth.

The craft were due to spend another hour flying side-by-side in a final effort to pinpoint year-old leaks in the Russian craft.

The leaks were the result of a collision on June 25 1997, between Mir and a Russian cargo vessel.

Final farewells

Unsuccessful attempts were made to locate them during the four-day hook up, when fluorescent gas was pumped into the damaged Spektr laboratory module.

But none of the nine astronauts could see any sign of it escaping into space and they agreed to try again when the uncoupling would make for better visibility.

Earlier on Monday, the two crews crammed themselves into Mir's small docking compartment to say final farewells.

They exchanged final handshakes and hugs in what was an emotional end to the three-year shuttle-Mir venture.

"You probably could tell it was kind of uncomfortable for us due to the nature of it, but we're sure proud of the whole programme," shuttle commander Charlie Precourt told mission control.

Parting gift

Mir commander Talgat Musabayev bid the shuttle crew "bye-bye". Mr Precourt responded with "dos vidaniya", Russian for "until we meet again".

As a parting gift for the shuttle astronauts, the Mir crew presented them with a wrench used on space-walks, with the instruction it was to be passed on to the first crew of the new international venture.

"It's a sort of relay stick from an old lady, station Mir, to the International Space Station," said Mr Musabayev said as he handed the large tool to Mr Precourt.

Discovery will bring home the last US astronaut, Andrew Thomas, who had been working aboard Mir since the end of January.

His two Russian counterparts - Mr Musabayev and Nikolai Budarin - will work aboard Mir until early August. The space station is due to be abandoned in December 1999.