US President Joe Biden has called Russian leader Vladimir Putin a butcher and explained how the US could help protect Ukraine from him.

Biden spoke at a pre-election event in North Carolina about the possibility of raising additional funds by increasing taxes for billionaires in the United States.

He noted that if billionaires paid a 25% federal tax rate, it could generate US$400 billion over the next 10 years.

"Imagine what we could do with that. We could do so many things – consequential  – including finally making sure that we take care of Ukraine from that butcher Putin," Biden said.

In February, Biden called Vladimir Putin a "crazy son of a bitch" during a fundraising event in San Francisco. The Kremlin called these words "shameful".

Additionally, Biden recently referred to Putin as a thug.