NASA said Tuesday it will pay $424 million more to Russia for giving US astronauts a lift to the International Space Station.

The hefty bill includes the training and transporting of six astronauts to and from the ISS in 2016 and the first half of 2017 in Russian Soyuz spacecraft.

That comes down to $70.6 million a seat, an increase of $5.6 million from the previous price tag.

NASA chief Charles Bolden pointed the finger squarely at the US Congress, saying that if it had approved the President Barack Obama's requested funding for a public-private partnership plan known as the "Commercial Crew Program" the US space agency would not have been forced to sign the new contract with its Russian counterpart Roscosmos.

"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 wrote in a blog post.

In the same entry, he stressed that full funding of $821 million -- as included in the administration's 2014 budget request -- was imperative to prevent further delays and keep the agency on track to meet its 2017 deadline.

"Even this delayed availability will be in question if Congress does not fully support the President's fiscal year 2014 request for our Commercial Crew Program, forcing us once again to extend our contract with the Russians," he wrote.

Russian Soyuz spacecraft are currently the only means of transport to the ISS for astronauts, since the end of NASA's shuttle program in July 2011.

"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," Bolden wrote.