Russian President Vladimir Putin has said that Moscow is “categorically against” the deployment of nuclear weapons in space.
His remarks came during a televised meeting with his defence minister, who also denied Russia had any such plans.
Last week US officials said Russia was developing a “troubling” new anti-satellite weapon which it was yet to deploy.
US media reports said it was space-based and armed with a nuclear warhead.
White House spokesman John Kirby said the US administration was taking the development “very seriously” and that President Joe Biden had already ordered “direct diplomatic engagement with Russia” over the threat.
Mr Putin called for international agreements on space weaponry to be adhered to and said Russia had offered many times to work jointly to strengthen them.
“Our position is clear and transparent. We have always been categorically against the deployment of nuclear weapons in space and we are still against it,” he said.
Defence Minister Sergei Shoigu said: “Firstly, we don’t have this [nuclear weapons in space]. Secondly, they know we don’t have it… but they’re still making a fuss.”
He repeated claims by Russian officials that the US pronouncements were a ruse to scare US lawmakers into passing additional Ukraine aid.
A group of Republicans in the House of Representatives has been holding up an aid package including a vital $60bn (£48bn) for Ukraine for several months.
Mr Kirby has strongly rejected Moscow’s claims.
Speaking a day after House Intelligence Committee chairman Mike Turner – a senior Republican – issued vague warnings of a “serious national security threat”, he told reporters that there was no immediate threat to the US public.
“We’re not talking about a weapon that can be used to attack human beings, or cause physical destruction, here on Earth,” he said.
While space weapons sound ripped from the pages of science fiction novels, military experts have long warned that space is likely to be the next frontier of warfare in an increasingly technology-dependent world.
They say Russia and China have been steadily developing military capabilities in space as they seek to catch up to the US.
The three countries already have the capability to attack satellites around the world. But, in theory, they cannot use nuclear weapons there.
All three are signatories of the Outer Space Treaty of 1967, which forbids countries from sending into orbit “any objects carrying nuclear weapons or any other kinds of weapons of mass destruction”.
But experts say the treaty provides no guarantee of safety in the current geopolitical climate because of Russia’s tendency to disregard its treaty obligations.
