US President Donald Trump cut short a meeting with Volodymyr Zelensky on Friday and said the Ukrainian leader is "not ready" for peace with Russia in an extraordinary meltdown in the Oval Office that threw question marks over chances for a truce.

Zelensky was meant to be making a full White House visit to sign a US-Ukrainian deal for joint exploitation of Ukraine's mineral resources, as part of a post-war recovery in a US-brokered peace deal.

Instead, an ugly clash blew up almost immediately in the Oval Office where Trump and Vice President JD Vance shouted at Zelensky, accusing him of not being thankful for US help in the three-year war against Russia.

Trump berated Zelensky, telling him to be more "thankful" and that without US assistance Ukraine would have been taken by Russia. "You're either going to make a deal or we're out," Trump added.

Zelensky left in his motorcade shortly after, without holding a planned joint press conference. The resources deal was left unsigned, the White House said.

Trump took to his Truth Social platform to castigate Zelensky saying "he is not ready for Peace," Trump wrote. "He can come back when he is ready for Peace."

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 - had appeared to get off to a friendlier start.

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

The clash left in doubt efforts led by Trump to cast himself as mediator in the war.

Speaking before the shouting match erupted, Trump told Zelensky that a truce is "fairly close." The US leader also said that the proposed minerals deal would be "very fair."

Russia's foreign ministry spokeswoman Maria Zakharova on Friday said Trump showed "restraint" by not hitting Ukrainian Zelensky during their shouting match in the White House. (AFP)