European leaders closed ranks Sunday in support of Kyiv at a London summit, where they pledged to spend more on security and assemble a coalition to defend any truce in Ukraine.

And French President Emmanuel Macron, flying back from the summit, said in a newspaper interview that France and Britain were proposing a one-month truce.

Bringing together 18 allies, the talks came just two days after US President Donald Trump berated Ukraine's Volodymyr Zelensky at a live White House news conference.

And UK Prime Minister Keir Starmer said that Britain, France "and others" would work with Ukraine on a plan to stop the fighting, which they would then put to Washington.

The London meeting came at a delicate moment for war-battered Ukraine, which faces uncertain backing from US President Donald Trump and is on the back foot against Russia's three-year invasion.

And Trump's row with Zelensky raised fresh questions over the US commitment to Ukraine and NATO.

Starmer said Europe found itself "at a crossroads in history."

"This is not a moment for more talk — it's time to act. It's time to step up and lead and unite around a new plan for a just and enduring peace," the premier said.

With no guarantee of US involvement, "Europe must do the heavy lifting," Starmer said. Several countries were ready to help defend any truce, he added — without naming them.

Macron, in an interview with France's Le Figaro newspaper, said he and Starmer were working on a one-month truce in Ukraine, "in the air, at sea."

He also suggested that European countries should raise their defence spending to between 3.0 and 3.5 percent of GDP to respond to Washington's shifting priorities.

Warm welcome in London

Zelensky was warmly embraced by many of the summit's attendees, including Starmer, Canadian Prime Minister Justin Trudeau and NATO chief Mark Rutte.

Outside the UK leader's home, demonstrators gathered to show their support for Ukraine, some dressed in the country's blue and yellow national colours.

His reception in London was in stark contrast to his reception at the White House two days earlier.

There, Trump accused Zelensky of not being grateful enough for US aid and not being "ready" for peace with Russia.

Their argument, played out in front of the world's news cameras, raised fears that Trump wanted to force Kyiv into a peace deal giving Russian President Vladimir Putin what he wants.

Starmer insisted the United States was "not an unreliable ally." Any deal "must have strong US backing" to succeed, he added.

But after the leaders gathered on Sunday, European Commission chief Ursula von der Leyen warned the continent urgently had to rearm to "prepare for the worst."

And Polish Prime Minister Donald Tusk called for the United States and Europe to show Putin "that the West has no intention of capitulating before his blackmail and aggression."

Starmer and France's President Emmanuel Macron have said they are prepared to deploy British and French troops to Ukraine to help preserve any truce.

But Italy's Prime Minister Giorgia Meloni — whose hard-right coalition government includes Moscow-friendly politicians — appeared to play down the possibility of Italy contributing soldiers.

"I see this as a solution that risks being very complex and probably less decisive than others," she said.

Rutte pointed to promises from more European countries to "ramp up defence spending," while insisting that Washington remained committed to the transatlantic alliance.

In addition to attending the security summit, Zelensky also met King Charles III at his Sandringham estate.

'Complete failure'

Friday's row in Washington marked a change from Zelensky's previous treatment there, where he was hailed as a Churchillian figure by the previous US administration.

Trump and his Vice President JD Vance angrily accused Zelensky of not being "thankful" and refusing to accept their proposed truce terms.

On Sunday, top Washington Republicans doubled down on their criticism of the Ukrainian leader, suggesting he may have to step down, underscoring Trump's stunning shift in approach to the war with Russia.

"We need a leader that can deal with us, eventually deal with the Russians, and end this war," Mike Waltz, Trump's national security adviser told CNN.

Republican Mike Johnson, speaker of the House of Representatives, said: "Either he needs to come to his senses and come back to the table in gratitude, or someone else needs to lead the country."

Trump has cast himself as a mediator between Putin and Zelensky, sidelining Kyiv and Europe while pursuing rapprochement with Putin.

Zelensky, though he did not apologise after the White House clash, indicated that he was still open to signing a deal on Ukraine's mineral wealth — coveted by Trump.

The US president on Sunday shared a reposting on his Truth Social platform arguing that the mineral agreement itself would give Ukraine the security it was seeking and that "in the end, Zelensky will have no choice but to concede."

Moscow meanwhile branded the Ukrainian leader's Washington trip a "complete failure" and said that Trump's changed stance "aligns" with its vision.