Russia says it will end cooperation with other nations on the International Space Station until the sanctions put on the country are lifted. Dmitry Rogozin, the head of Russian space agency Roscosmos, announced in a thread on Twitter that the “restoration of normal relations between partners” on the ISS and other projects is only possible with the “complete and unconditional lifting of illegal sanctions.”

In translated versions of his tweets, Rogozin says he appealed the sanctions in letters to NASA, the European Space Agency, as well as the Canadian Space Agency. Rogozin also posted images of what appears to be each country’s response — the CSA confirmed the letter’s authenticity to The Verge but declined to comment any further. The Verge also reached out to the ESA but didn’t immediately hear back.

While NASA didn’t directly confirm the letter’s authenticity, the agency did acknowledge Rogozin’s comments and maintains that the ISS is still operating with Roscosmos’ input. “NASA is aware of recent comments regarding the International Space Station. U.S. sanctions and export control measures continue to allow U.S.-Russia civil space cooperation on the space station,” NASA Administrator Bill Nelson’s statement reads. “The professional relationship between our international partners, astronauts and cosmonauts continues for the safety and mission of all on board the ISS.”

The CSA’s letter has a similar response to Rogozin’s request, stating, “I can assure you that Canada continues to support the ISS program, and is dedicated to its safe and successful operations.” Meanwhile, ESA head Josef Aschbacher replied by saying he’ll pass on Rogozin’s request to the agency’s member states for assessment.

“The position of our partners is clear: the sanctions will not be lifted,” Rogozin says. “The purpose of the sanctions is to kill the Russian economy, plunge our people into despair and hunger, and bring our country to its knees.” Rogozin adds that Roscosmos will soon determine a date on when to halt Russia’s involvement with the ISS, which will then be reported to Russian government officials.

Rogozin reacted strongly to the sanctions imposed by President Joe Biden in February, making an insinuation that the space station could come crashing down to Earth without Russia’s involvement. As my colleague Loren Grush points out, Russia’s withdrawal from the station has the potential to do real harm, as NASA relies on Russia to maintain the ISS’s position and orientation in space.

Roscosmos has an agreement with NASA to cooperate on the ISS through 2024. Last year, the Biden administration announced plans to extend the ISS program until 2030, which Russia hasn’t signed on with yet. NASA said Russia was “moving toward” extending its cooperation, but Rogozin’s statements make this seem unlikely. Earlier this week, NASA astronaut Mark Vande Hei safely returned to Earth aboard a Russian Soyuz rocket with two cosmonauts. Prior to his arrival, there had been concerns about his return home amid Russia’s ongoing war in Ukraine, but Roscosmos maintained that it would not strand Vande Hei on the ISS.

Update April 2nd, 2022 4:46PM ET: Updated to add confirmation from the CSA about the authenticity of the CSA letter that Dmitry Rogozin posted on Twitter.

Update April 4th, 2022 11:25AM ET: Updated to add a statement from NASA Administrator Bill Nelson.