Washington DC - US President Donald Trump and Volodymyr Zelensky openly argued in the White House on Friday as they clashed on the need for compromising with what the Ukrainian president called Russia's "killer" leader.

Trump furiously berated Zelensky as they sat in the Oval Office, telling him to be more "thankful" and saying, "You're in no position to dictate what we're going to feel."

And he told the Ukrainian president that he either "make a deal" with Russia "or we're out."

US Vice President JD Vance, sitting nearby, also attacked Zelensky, calling him "disrespectful."

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Zelensky appeared to try to speak but was cut off.

The extraordinary outburst came after Trump said Ukraine will have to make "compromises" in a truce with Russia, which launched a full-scale invasion of its neighbor three years ago.

"You can't do any deals without compromises. So certainly he's going to have to make some compromises, but hopefully they won't be as big as some people think," Trump said.

But showing Trump pictures of war atrocities and referring to President Vladimir Putin, Zelensky said there should be "no compromises with a killer on our territory."

"Crazy Russians," he said, deported Ukrainian children and committed war crimes during their three-year invasion of his country.

Trump lashed out at Zelensky, who he said was "not acting at all thankful" and not "nice."

"You're gambling with the lives of millions of people," Trump said. "You're gambling with World War Three, and what you're doing is very disrespectful to the country – this country."

The dramatic public breakdown in the long-tense relationship between Zelensky and Trump came after their meeting – in front of a large group of journalists – appeared to get off to a somewhat friendlier start.

Zelensky had said, "I think President Trump is on our side."