US President Joe Biden said Thursday the world risks nuclear "Armageddon" for the first time since the Cold War, claiming that he is trying to find Russian President Vladimir Putin's "off-ramp" in the Ukraine war.

"We have not faced the prospect of Armageddon since Kennedy and the Cuban missile crisis" in 1962, Biden said at a Democratic Party fundraising event in New York, referring to former US President John F Kennedy.

The US President said Putin is "not joking" when he threatens to use nuclear weapons.

Biden considered that for the "first time since the Cuban missile crisis, we have a direct threat from the use of nuclear weapons if in fact things continue down the path they are going."

"We're trying to figure out what is Putin's off-ramp," he added.

"We've got a guy I know fairly well," Biden said. Putin's "not joking when he talks about potential use of tactical nuclear weapons or biological or chemical weapons, because his military is, you might say, significantly underperforming."

But "I don't think there's any such thing as the ability to easily (use) a tactical nuclear weapon and not end up with Armageddon," the US President indicated.

On September 21, Biden accused Russia of violating the core tenets of membership in the United Nations over the war in Ukraine, claiming that Moscow was making "irresponsible" threats to use nuclear weapons.

During his speech at the United Nations General Assembly in New York, Biden criticized Russian President Vladimir Putin over the war.

"Again, just today, President Putin has made overt nuclear threats against Europe, in a reckless disregard for the responsibilities of the nonproliferation regime," he said.

"A nuclear war cannot be won, and must never be fought," Biden told the UN General Assembly, saying that Moscow made "irresponsible nuclear threats."

It is noteworthy that the White House confirmed on October 1 that Biden signed a bill approving appropriations through December 16, 2022, including an additional $12.4 billion to support Ukraine.

US DoD: No evidence that Russia will use nuclear weapons in Ukraine

However, contradicting Biden's claims, US Defense Secretary Lloyd Austin last week said that there is no evidence in sight that suggests that Russia intends to use nuclear weapons in Ukraine.

During an interview with CNN, Austin said, "I don't see anything right now that would lead me to believe that he [Russian President Vladimir Putin] has made such a decision." 

He added that Washington had previously passed on these concerns to Moscow via high-level channels.

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