Russian cosmonauts successfully completed a six-hour spacewalk to build up the meteorite defences of the International Space Station (ISS) and repair a navigation antennae, officials said on Thursday.

"Cosmonauts successfully dealt with the scheduled task. They set up additional anti-meteorite panels on the ISS's Russian segment and replaced the old high-frequency cable" for the antennae, a spokesperson for the mission control centre outside Moscow said, as quoted by RIA Novosti.

Fyodor Yurchikhin and Oleg Kotov began their mission at 11.09pm Moscow time (7.09pm GMT) instead of 10.20pm as scheduled, as they had to lower pressure in the docking block, Russian space officials earlier said.

The spacewalk was being monitored from within the ISS by US astronaut Sunita Williams and on the ground at the mission control centre.