US National Security Adviser Jake Sullivan said on Friday that Washington takes Russian President Vladimir Putin's nuclear threats seriously but does not presently see indications of the use of nuclear weapons by Russia.

"There is a risk, given all the loose talk and nuclear saber rattling by Putin, that he would consider this and we’ve been equally clear about what the consequences would be," Sullivan told reporters, but added, "We do not presently see indications about the imminent use of nuclear weapons."

Asked if the US would actively enter the war if Putin used nukes on Ukraine, Sullivan replied, "So, I have said before that we have had the opportunity to communicate directly to Russia a range of consequences...and the kinds of actions the United States would take."

Putin issued a thinly veiled nuclear threat in a recent speech in which Putin also announced his country's first wartime military mobilization since World War Two.

US President Joe Biden, in his speech at the United Nations General Assembly, accused Putin of making "overt nuclear threats against Europe" in reckless disregard for nuclear nonproliferation responsibilities.

Sullivan on Sunday warned that the United States would respond decisively to any Russian use of nuclear weapons against Ukraine and has spelled out to Moscow the "catastrophic consequences" it would face.

"If Russia crosses this line, there will be catastrophic consequences for Russia. The United States will respond decisively," Sullivan told NBC's "Meet the Press" program.

He did not describe the nature of the planned US response in his comments on Sunday but said the United States has privately to Moscow "spelled out in greater detail exactly what that would mean."

(Israel National News' North American desk is keeping you updated until the start of Shabbat in New York. The time posted automatically on all Israel National News articles, however, is Israeli time.)