President Joe Biden said on Thursday the risk of nuclear "Armageddon" was the highest for 60 years, when Russian President Vladimir Putin renewed his threats as his military withdrawal to Ukraine.
In remarks at a reception of the Democratic Senatorial Campaign Committee, Biden said it was the first time since the 1962 Cuban missile crisis that there has been a "direct threat" of nuclear.
"We have not faced the prospect of Armageddon since Kennedy and the Cuban missile crisis," he said, making his scathing remarks about the use of nuclear weapons since Russia's invasion of Ukraine in February. "
Late last month, Putin renewed the nuclear threats he had made at the start of Russia's invasion. "If the territorial integrity of our country is threatened, we will certainly use all means at our disposal.
Putin issued his warning when he announced the withdrawal of 300,000 Russian troops after his military forces suffered a severe setback on the battlefield in Ukraine.
This week Kiev's troops were advancing east and south of the country, threatening a major new breakthrough and forcing Putin's troops to retreat from the territory they claimed.
With increasing pressure on those defeats and chaotic mobilisation at home, fears have intensified that he may be willing to go further instead of giving up.
"We have a guy I know well. He's not kidding when he talks about tactical nuclear weapons or the possible use of biological or chemical weapons because he has an army that you can significantly underperform. "