American astronauts will continue to fly to the International Space Station aboard Russian spacecraft through 2017, NASA said Wednesday.

"Until a US commercial vehicle is sustained, continued access to Russian crew launch, return, and rescue services is essential for planned ISS operations," NASA said in a procurement announcement.

The agency intends to buy six more seats on Russian Soyuz spacecraft to ferry American astronauts to the ISS in 2017.

NASA will also contract with the Russian space agency Roscosmos to have seats available on docked Soyuz craft through spring 2018 in the event of an emergency evacuation of the station.

The cost of the proposed deal was not disclosed, but NASA signed a contract with Roscosmos last spring to pay about $70 million per seat for launch services through early 2017.

The agency, which is funding the development of several manned spacecraft, plans to select a commercial launch provider for missions starting in 2017.

Two NASA-funded private spacecraft - SpaceX's Dragon and Orbital Sciences Corp.'s Cygnus - have already made unmanned resupply missions to the ISS.

No American vehicle has taken astronauts into orbit since the decommissioning of NASA's shuttle fleet in 2011. The Soyuz is one of only two operational orbital manned spacecraft in the world, the other being China's Shenzhou.

Source: RIA Novosti