The US accused Russia of testing an anti-satellite weapon in space and warned that the threat to Washington's systems was "real, serious, and growing".
The US space command said it had "evidence" that Moscow "carried out a non-destructive test of a space-borne anti-satellite weapon on July 15".
"Last week's test is another example of how the threats to U.S. and Allied space systems are real, serious, and growing," the Thursday statement continued.
"This is clearly unacceptable," US nuclear negotiator Marshall Billingslea tweeted, adding that this is a "big problem" that will be discussed next week in Vienna, where he will discuss a successor to the new START contract speaks.
The contract limits the nuclear warheads of the United States and Russia – the two superpowers from the Cold War era.
Kremlin spokesman Dmitri Peskow commented on the allegations on Friday, saying that Russia supports "the complete demilitarization of space and no weapons in space".
The US Space Command said the test consists of the Russian Cosmos 2543 satellite, which injects an object into orbit.
Russian state media have reported that Cosmos-2543 was deployed by another satellite, Cosmos-2542, launched by the Russian military on November 25, 2019.
The Ministry of Defense said the satellite was meant to "monitor the condition of Russian satellites," but the state-run daily Rossiyskaya Gazeta said it had the ability to "receive information from other people's satellites."
The system is the same that Space Command raised concerns earlier this year when it was maneuvering near a U.S. government satellite, said General Jay Raymond, director of U.S. Space Command.
"This is further evidence of Russia's continued efforts to develop and test space-based systems, and is in line with the Kremlin's military doctrine of using weapons that threaten US and Allied space assets," Raymond said in a statement.
It is the most recent example of Russian satellites behaving "contrary to their declared mission," added the statement by the space command.
"This event underscores Russia's hypocritical commitment to arms control in space," said Christopher Ford, US Secretary of State for Arms Control.
The explanation also came when China launched a rover to Mars on Thursday, a trip that coincided with a similar U.S. mission when the powers launched their rivalry into space.
(Except for the headline, this story was not edited by NDTV staff and published from a syndicated feed.)