(NewsNation) — After nearly three decades of close collaboration between Russia and the West on the International Space Station, that partnership could be coming to an end, potentially stranding the last American at the ISS in space.

American astronaut Mark Vande Hei was set to return to Earth in three weeks on a Russian spacecraft but now that journey is in doubt as tensions escalate between the United States and Russia.

The head of Russia’s space agency appeared to issue a number of threats after the U.S. imposed sanctions against the country for its invasion of Ukraine.

“If you block cooperation with us, who will save the International Space Station from an uncontrolled deorbit and fall into the United States or Europe?,” Dmitry Rogozin, the head of Russia’s Space Agency, reportedly said in a number of tweets.

“There is also the possibility of a 500-ton structure falling on India and China. Do you want to threaten them with such a prospect? The ISS does not fly over Russia, therefore all the risks are yours, are you ready for them?,” Rogozin continued.

Vande Hei is set to return after 300 days at the International Space Station. He, along with two Russian cosmonauts, are scheduled to land in Kazakhstan.

NASA said plans for Vander Hei’s return have not changed and did not comment on the Russian threats.

The International Space Station, which has long been celebrated as a successful example of international collaboration, has led to some of the most important scientific discoveries of the 21st century since its launch in 1998.

The station is divided into two segments: the United States Orbital Segment (USOS) operated by the U.S. and the Russian Orbital Segment (ROS) operated by Russia.

Since the war began, Russian officials have threatened to crash the space station and refused to launch satellites over Western countries.

Last week, Russia grounded 36 internet satellites scheduled for launch in response to the sanctions imposed on them. Russia’s space agency was contracted to carry the satellites into orbit aboard a Soyuz rocket.

There are concerns that Russian aggression in space could directly affect the war in Ukraine — satellite imagery is crucial intelligence and helps nations across the world understand what’s going on in the country.

Russia has also stopped supplying rocket engines to the United States in retaliation for the Biden administration’s economic sanctions.

“Let them fly on something else … their broomsticks,” Rogozin said.