US President Joe Biden said the world faces the "prospect of Armageddon" with Russian President Vladimir Putin threatening to use nuclear weapons to protect Russian territory.

Biden said the Russian president was "not joking when he talks about potential use of tactical nuclear weapons or biological or chemical weapons, because his military is, you might say, is significantly underperforming."

"For the first time since the Cuban Missile Crisis, we have a direct threat to the use of nuclear weapons, if in fact things continue down the path they'd been going," the US president said in New York on Thursday.