The cost of a ride to the International Space Station (ISS) just shot up like a rocket.

NASA will pay $US70.7 million ($A68.50 million) to Russia for each astronaut Moscow's space agency ferries into orbit in 2016 and 2017, the US space agency said.

NASA and Roscomos signed a $US424 million agreement to bring six US astronauts aloft for long-term mission aboard the ISS. The deal would cover all training, launch preparation, flight operation, landing and if needed rescue efforts.

The previous agreement had set the price at $US62.7 million per seat through 2015.

The US has been reliant on the Russian Soyuz craft to bring its astronauts into orbit since the retirement of its space shuttle fleet in 2011. The US is supporting the development of commercial spacecraft, which have so far delivered cargo to the ISS, but are not yet ready to carry crew.

'While our Russian counterparts have been good partners, it is unacceptable that we don't currently have an American capability to launch our own astronauts,' NASA Administrator Charles Bolden said.

He blamed politicians for not sufficiently funding the commercial crew program, leaving it short of its goal of ferrying astronauts by 2015, and instead forcing a continued reliance on Russian cooperation.

'If NASA had received (President Barack Obama's) requested funding for this plan, we would not have been forced to recently sign a new contract with Roscosmos for Soyuz transportation flights,' he wrote on a NASA blog.

'Because the funding for the president's plan has been significantly reduced, we now won't be able to support American launches until 2017.'

He warned further funding reductions could further delay the United States' return to spaceflight and asked Congress to allocate Obama's full $US821 million budget request.

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NASA to pay Russia $68m per rocket seat