Russia, responding to American sanctions imposed in the Ukraine crisis, is threatening to pull out of using the International Space Station in 2020 and says it will refuse to transport American astronauts to it.

While the countries are cooperating in staffing the station, Russia's Soyuz spacecraft are currently the only way to transfer crew members to and from the ISS following the cancellation of America's space shuttle program.

Russia's announcement comes following U.S. sanctions against it for its intervention in the Ukraine crisis, including a denial of export licenses covering high-tech systems needed by Russian industry.

"These sanctions are out of place and inappropriate," Deputy Prime Minister Dmitry Rogozin said in announcing the ISS decision. "We have enough of our own problems."

He also said Russia would stop supplying the RD-180 and NK-33 rocket engines used to lift U.S. military satellites into orbit.

Rogozin oversees the government-controlled company that supplies RD-180 engines to the U.S. United Launch Alliance (ULA), the Boeing and Lockheed-Martin joint venture that uses the Russian engines in the first stage of the Atlas V launch rocket.

The ULA, in a statement, said it is "hopeful that our two nations will engage in productive conversations over the coming months that will resolve the matter quickly."

The United States hopes to maintain the ISS in operation until 2024, four years beyond its original target mission, and NASA is reportedly working to supply an American transport capability to take crew to the space station using commercially spacecraft being developed by companies such as Sierra Nevada and SpaceX.

Despite Rogozin's announcement, nothing has immediately changed in the cooperation of the Russian Federal Space Agency, known as Roscosmos, and NASA.

On May 13, three ISS crewmembers, one Russian, an American and a Japanese, left the station in a Russian Soyuz crew capsule, touching down in Kazakhstan.

"Ongoing operations on the ISS continue on a normal basis," NASA spokesman Allard Beutel said in a statement. "We have not received any official notification from the government of Russia on any changes in our space cooperation at this point."

Whether the Russian announcement will in fact be translated into action remains to be seen, U.S. experts say.

"Part of me thinks it is posturing," says Roger Launius, an associate director at the National Air and Space Museum in Washington. "They're talking about beyond 2020. There's a world of time between now and then."