Russia's space agency on Saturday demanded an explanation after NASA put off a planned visit to the United States by Russia's controversial space chief.
Dmitry Rogozin, a firebrand nationalist politician known for his anti-Western rhetoric, was set to visit the US in February but NASA said Friday that it was postponing his visit indefinitely.
Rogozin, appointed by President Vladimir Putin in May last year and previously a deputy prime minister, is blacklisted and under US sanctions over Russia's actions in Ukraine.
Russia's Roscosmos space agency said in a statement that "it expects official explanations of NASA's position" and stressed that Rogozin's visit was planned "in accordance with an invitation received earlier." It added a veiled warning that preparations for talks on cooperation with the US on the ISS programme and deep space exploration are "so far not suspended."