The United States issued a stern warning to Russia following a nuclear threat from President Vladimir Putin last week.
US National Security Adviser Jake Sullivan said the country would respond firmly to any Russian use of nuclear weapons against Ukraine.
Last week, President Putin announced the deployment of paramilitary forces and issued a nuclear threat to Ukraine.
In a speech on Sunday, Jake Sullivan also said that there would be 'catastrophe' for Russia if it overstepped the mark. However, he did not explain how it would react to Russia.
But according to him, America has expressed privately what it means to Russia, given that Washington has often been in direct contact with Moscow including in the last few days to discuss the situation in Ukraine and Putin's actions and threats.
Meanwhile in a separate development, the US and its allies continue to funnel aid to Ukraine amid growing threats of war by Russia.
Most recently, Ukrainian President Voldymyr Zelensky thanked America after receiving NASAMS (National Advance Surface-to-Air Missile Systems) air defense missiles.
