The United States National Security Adviser Jake Sullivan said the U.S. would respond decisively to any Russian use of nuclear weapons against Ukraine.

Mr Sullivan told NBC’s meet the press programme that “if Russia crosses this line, there will be catastrophic consequences for Russia. The United States will respond decisively.”

His remarks represented the latest American warning following the thinly veiled nuclear threat made by Vladimir Putin last Wednesday in a speech in which the Russian president also announced his country’s first wartime military mobilisation since World War II.

In his comments on Sunday, Mr Sullivan did not describe the nature of the planned U.S. response but said the United States has privately to Moscow “spelt out in greater detail exactly what that would mean.”

According to him, the United States has been in frequent, direct contact with Russia during the last few days to discuss the situation in Ukraine and Mr Putin’s actions and threats.

Mr Sullivan added, “Putin remains intent on wiping out the Ukraine people that he does not believe have a right to exist. So he’s going to keep coming, and we have to keep coming with weapons, ammunition, intelligence and all the support we can provide.” 

In a speech at the United Nations General Assembly in New York on Wednesday, U.S. President Joe Biden accused Mr Putin of making “overt nuclear threats against Europe” in reckless disregard for nuclear non-proliferation responsibilities.

Russia also was staging a referendum in four eastern Ukrainian regions to annex territory that Russian forces had taken during their invasion of Ukraine launched in February.

Ukraine and its allies have called the referendums a sham designed to justify an escalation of the war and Mr Putin’s mobilisation drive after recent battlefield losses.

Experts said by incorporating the areas of Luhansk, Donetsk, Kherson and Zaporizhzhia into Russia, Moscow could portray attacks to retake them as an attack on Russia itself, a warning to Ukraine and its Western allies.

However, after suffering setbacks on the battlefield, Mr Putin mobilised 300,000 troops while threatening to use “all available means” to protect Russia.

“This is not a bluff,” Mr Putin said in remarks viewed on the world stage as a threat to use nuclear weapons.

(Reuters/NAN)