MOSCOW - A pair of Russian cosmonauts and a US astronaut sealed themselves inside a Russian Soyuz capsule on Monday and left the International Space Station, ending a six-month mission, officials said.

With former station commander Oleg Kotov at the controls, the Soyuz slipped away from its berthing port at 8:02 a.m. (Singapore time)

Touchdown is expected at 11:24 p.m. southeast of Dzhezkazgan, Kazakhstan.

Strapped inside the Soyuz with Kotov are station flight engineers Sergei Ryazansky and NASA's Michael Hopkins.

The trio launched together into space on Sept 25.

"It was a really good increment," Kotov said during a change-of-command ceremony broadcast on NASA Television on Sunday.

In addition to working on dozens of science experiments, Kotov and Ryazansky carried the Olympic torch for the 2014 Winter Olympic Games outside the station during a spacewalk on Nov. 9.

They leave behind a small crew headed by Japan's Koichi Wakata, the first Japanese national to command the station.

Three more crew members are due to arrive later this month.

Severe weather in Kazakhstan had threatened to delay the Soyuz's landing.

Earlier on Monday, fog and low visibility had prevented airborne rescue and recovery teams from getting to Zhezkazgan, a town about 150 km from the remote landing site on the windswept flatlands, a Russian space industry source said.

But Russian officials decided to go ahead with the landing after reviewing weather forecasts and the status of recovery crews.

"There's a lot of snow on the ground and temperatures are hovering in the single-digits (Fahrenheit,)" said NASA mission commentator Dan Huot.

The US-Russian space partnership so far has not been affected by tensions over Ukraine. The countries lead the 15-nation space station program.

The US$100 billion (S$126 billion) research complex, which flies about 418 km above Earth, has been permanently staffed by rotating crews of astronauts and cosmonauts since November 2000.