After Russian President Vladimir Putin stated days ago that he was "not cheating" when he spoke of his willingness to use nuclear weapons if Russia felt that its territorial integrity was under threat, the Kremlin said that intermittent contacts had taken place between Russia and the United States on nuclear weapons issues

Kremlin spokesman Dmitry Peskov said the two sides maintained an open but limited channel of dialogue to allow "emergency messages to be exchanged" between the world's two largest nuclear powers.

Peskov told reporters that "there are channels for dialogue at the right level but they are of a very sporadic nature, allowing at least some emergency messages to be exchanged about each side's position".

As he announced a mobilization campaign that clearly threatened to escalate the seven-month conflict in Ukraine, Putin said last week that Moscow was willing to use nuclear weapons to protect its territory and people

On Sunday, the United States warned Russia of catastrophic consequences if nuclear weapons were used in Ukraine.

US National Security Adviser Jake Sullivan said his country would "respond decisively" if Russia used these weapons against its neighbour, and did not elaborate, but said Washington had told Moscow in private chats "what that meant specifically in more detail."

Peskov declined to comment when asked what the United States had revealed to Russia what it meant by "catastrophic consequences".

Ukrainian President Volodymyr Zelenskiy said he did not believe his Russian counterpart, Vladimir Putin, was deceitful when he said Moscow would be prepared to use nuclear weapons to defend Russia.

Zelensky, who has previously downplayed such warnings as nuclear blackmail, told C. B. S-News, Sunday, "Look, maybe yesterday it was a hoax, now, it could be real."