Donald Trump has warned Volodymyr Zelensky he is “gambling with World War Three” in a heated exchange at the White House, amid UK efforts to broker an American security guarantee for Ukraine.

The US president met his Ukrainian counterpart in the Oval Office as the two nations were set to sign a deal granting the US access to rare minerals in exchange for further military aid.

Sir Keir Starmer is preparing to discuss how to guarantee that a peace deal in Ukraine will last when he meets Mr Zelensky and other European leaders in Downing Street this weekend.

But the relationship between the Ukrainian leader and Mr Trump remains tense, after the US president last week accused Mr Zelensky of being a dictator.

As the US president met his counterpart in the Oval Office, their discussions became heated.

“You’re gambling with millions of people … You’re gambling with World War Three,” Mr Trump said.

Mr Zelensky warned the US would “feel it in the future” if it did not continue to support Ukraine.

“Don’t tell us what we’re going to feel. We’re trying to solve a problem,” Mr Trump hit back.

US vice president JD Vance questioned why Mr Zelensky had not said thank you for US military aid during the meeting.

Mr Vance was also heard to say to the Ukrainian leader: “Mr President, with respect, I think it’s disrespectful for you to come into the Oval Office and try to litigate this in front of the American media.

“Right now, you guys are going around and forcing conscripts to the front lines because you have manpower problems. You should be thanking the president for bringing an end to this conflict.”

The fractious meeting comes after Sir Keir and France’s president Emmanuel Macron travelled to Washington DC for talks with Mr Trump.

The British and French leaders sought to charm the US president and were met with a warm welcome.

Downing Street has welcomed the US-Ukraine minerals deal, as it would “bind” Washington to Kyiv.

Ahead of Sunday’s summit focused on security, the Prime Minister will meet with Mr Zelensky separately.

A Downing Street spokesman said on Friday that “the UK has made it clear that we’ll play our full part in ensuring a just and lasting peace deal on Ukraine’s terms, backed up by strong security guarantees”.

“Just this week we demonstrated our commitment to that, confirming we’ll increase defence spending to 2.5% by 2027. But that peace deal has to come first and as you know, the Prime Minister will meet President Zelensky before convening European leaders in London on Sunday to continue those discussions,” he said.

“The deal has to come first, but our teams are going to be talking about how we make sure that deal sticks and is lasting and enforced.”

The continued diplomacy push over the weekend comes after Sir Keir’s meeting with Mr Trump at the White House on Thursday.

The US president has continued to resist calls to fully commit American military might to guarantee any Ukraine peace deal, but he has suggested closer economic ties and an agreement on mineral access between Kyiv and Washington would effectively act as a security “backstop”.

Sir Keir returned to the UK on Friday following a trip to the White House which went as well as No 10 could have hoped, with Mr Trump clearly pleased with the King’s invitation for an unprecedented second state visit, giving an indication that he would not block the Chagos Islands deal and suggesting a trade deal could spare British exports from US tariffs.

As well as the meeting with Mr Zelensky, Sunday will see the Prime Minister meet separately with Italy’s Giorgia Meloni and chair a call with the Baltic countries – Latvia, Lithuania and Estonia – before hosting the summit.

Mr Zelensky, Mr Macron and Ms Meloni have been invited to the summit along with leaders from Germany, Denmark, the Netherlands, Norway, Poland, Spain, Turkey, Finland, Sweden, the Czech Republic and Romania, as well as the Nato secretary general and the presidents of the European Commission and European Council.

They will discuss the next steps in planning for security guarantees if a Ukraine peace deal is reached – something Sir Keir believes will have to involve the US.

The leaders will consider how to strengthen Ukraine’s current position, with military support and increased economic pressure on Russia.

The UK wants US military assets to provide surveillance, intelligence and – potentially – warplanes providing air cover to deter Russian president Vladimir Putin from launching another bid to conquer his neighbour.

In Washington on Thursday, Mr Trump said: “Well, there is a backstop. First, you have European countries, because they’re right there, we’re very far away, we have an ocean between us.

“But we want to make sure it works.”

He continued: “We are a backstop because we’ll be over there, we’ll be working in the country.”

The president and the Prime Minister agreed to begin work on a new US-UK economic deal after Sir Keir dangled the carrot of an unprecedented second state visit to woo Mr Trump.

Sir Keir said the two leaders had decided “to begin work on a new economic deal with advanced technology at its core”.

The president, who is set to impose a 25% import tax on UK steel in March, said: “We could very well end up with a real trade deal where the tariffs wouldn’t be necessary.”

It is understood the proposed agreement is likely to focus on technology, rather than being an all-encompassing free trade deal.