Joe Biden on Thursday warned the risk of nuclear "Armageddon" was at its highest level since the 1962 Cuban Missile Crisis, as Russia hinted at the possibility of using tactical nuclear weapons after suffering major setbacks in its invasion of Ukraine.

Speaking at a fundraiser for the Democratic Senatorial Campaign Committee on Thursday, Mr Biden said Russian President Vladimir Putin was "a guy I know fairly well" and Putin was "not joking when he talks about the use of tactical nuclear weapons or biological or chemical weapons."

"We have not faced the prospect of Armageddon since Kennedy and the Cuban Missile Crisis," he said.

He added the threat from Putin was real because the Russian military seemed to be "significantly underperforming". 

US officials have warned for months that Russia could turn to weapons of mass destruction in Ukraine as it faces a series of strategic setbacks on the battlefield.

The UN nuclear safety inspection team at Zaporizhzhia plant is expected to double in size to four later today.

Two International Atomic Energy Agency inspectors stationed at the Russian-controlled site will be replaced by a team of four, a local Moscow-installed official Alexander Volga told Russian news agency TASS.

He added that power units at Europe's largest nuclear plant will be recommissioned subject to routine maintenance.

Two Russians attempting to avoid being drafted to military duty in Ukraine sailed 300 miles through rough waters on a small boat to claim asylum in Alaska.

The pair immediately applied for refuge from the US state upon landing on a remote Alaskan island in the Bering Sea.

A spokesperson for Alaska Senator Lisa Murkowski's office said: "The Russian nationals reported that they fled one of the coastal communities on the east coast of Russia to avoid compulsory military service."