Armed interior ministry forces patrolled the train tracks at Russia's Baikonur cosmodrome on Wednesday, amid heightened security ahead of a launch to the International Space Station.

The Soyuz rocket set to blast off on Friday was rolled out of its hangar and out across the barren Kazakh steppe under tighter than normal security two days after a pair of suicide bombers killed dozens in the Moscow metro.

Base officials told journalists at the site to expect tighter-than-normal controls on their movements and security personnel were carrying out document checks throughout the facility in contrast to routine practice.

Security is always high at strategically-sensitive Baikonur, the historic launch site where Yuri Gagarin blasted off in 1961 to become the first human in space, but security was visibly tighter than usual following the bombings.

Sniffer dogs checked the tracks for improvised explosive devices and a helicopter swooped low overhead in the pale early morning light as the 50-metre (160-foot) vessel was dragged to the launch pad by an aging locomotive.

Russian cosmonauts Alexander Skvortsov and Mikhail Kornienko, together with US astronaut Tracy Caldwell Dyson, are to take off Friday on a six month mission which will bring the ISS back up to its six person long-term capacity.

Among the key aims of their mission are the repair of the water recovery system apparatus on the ISS, which has been faltering in recent weeks, and to bring additional life support systems, NASA spokesman Rob Navias told AFP.

Their arrival comes less than a week before the US space shuttle Discovery is set to arrive at the ISS, which will cut short the amount of time the crew will have to acclimatize to conditions aboard the station.

Russia built the Baikonur cosmodrome on the arid plains of Kazakhstan in Soviet times and has continued to use the site under a rental deal since Kazakhstan became independent after the collapse of the Soviet Union in 1991.