US President Biden denounces Putin as 'murderous dictator'

US President Joe Biden has called Russia's President Putin a "murderous dictator."

"The republic is standing together against a murderous dictator, a pure thug who is waging an immoral war against the people of Ukraine," Biden said in Washington on Thursday to mark St Patrick's Day.

"And Putin is paying a big price for his aggression," Biden continued shortly afterwards.

Biden had already sharpened his tone on Wednesday, calling Putin a "war criminal". White House spokesperson Jen Psaki said afterwards that he spoke from his heart.

Biden now spoke of "an inflection point in history" in light of Russia's war of aggression on Ukraine. This only happens every few generations, he said.

"I think we're in a genuine struggle between autocracies and democracies, and whether or not democracies can be sustained."