US warns Russia not to use nuclear weapons against Ukraine (symbolic photo).

Washington:

US National Security Adviser Jake Sullivan said today that the US will resolutely respond to any use of nuclear weapons by Russia against Ukraine.

He has warned Moscow of "disastrous consequences".

Last Wednesday, there were indications of the threat of a nuclear attack from Vladimir Putin.

The Russian president also announced his country's first wartime military mobilization since World War II.

After this Sullivan's comment came as a warning to America. 

According to the news agency Reuters

, Jake Sullivan told NBC's "Meet the Press" program that, "If Russia crosses this border, it will have disastrous consequences. America will respond decisively." 

Sullivan did not mention the US's specific response in his remarks today, but said the US privately told Moscow "in more detail what that would mean."

Sullivan said the US has been in constant direct contact with Russia.

During the last few days, the situation in Ukraine and the steps and threats of Russian President Putin have also been discussed.

US President Joe Biden, in a speech at the United Nations General Assembly in New York on Wednesday, accused Vladimir Putin of dereliction of responsibility for nuclear non-proliferation and of being "an open nuclear threat against Europe".

Russia is also holding a referendum in four eastern Ukrainian regions.

Russian forces have occupied these areas after launching an invasion of Ukraine in February.

Ukraine and its allies have called the referendum a sham to justify Putin's campaign of mobilization after a recent battlefield defeat.


Russian President threatens Western countries with nuclear weapons