WASHINGTON, April 30  – NASA will pay an additional $424 million to extend its contract with Russia’s Federal Space Agency (Roscosmos) to transport US astronauts to and from the International Space Station (ISS), NASA said Tuesday, a move that America’s space chief said underscores how diminished funding is hampering the US space program.

“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 wrote in a blog post Tuesday.

The United States has relied on Roscosmos to transport its astronauts to and from the ISS aboard Soyuz spacecraft ever since the US Space Shuttle Program was shuttered in 2011.

The extended deal inked between the two agencies will allow US astronauts to travel aboard Russian spacecraft to the ISS through 2016 and will include return and rescue services through June 2017, NASA said in a statement Tuesday.

Bolden wrote that lack of Congressional funding has stymied the so-called Commercial Crew Program — supported by US President Barack Obama’s administration—which was proposed three years ago to have domestic firms send American astronauts into space by 2015.

“It’s a plan that supports the US human spaceflight program, boosts our economy, and helps create good-paying American jobs,” Bolden wrote Tuesday. “If NASA had received the president’s requested funding for this plan, we would not have been forced to recently sign a new contract with Roscosmos for Soyuz transportation flights.”

“Because the funding for the President’s plan has been significantly reduced, we now won’t be able to support American launches until 2017,” Bolden added.

The extended deal also includes “comprehensive Soyuz support, including all necessary training and preparation for launch, flight operations, landing and rescue of six space station crew members on long-duration missions,” NASA said Tuesday.