LONDON — Donald Trump’s Friday meeting with Russian President Vladimir Putin provides “a viable chance” to end the war in Ukraine — but Putin must “prove he is serious about peace, Downing Street said.

U.K. Prime Minister Keir Starmer on Thursday hosted Ukrainian President Volodymyr Zelenskyy in Downing Street ahead of the U.S. president’s Alaska meeting with Putin to discuss how the war in Ukraine can be ended three and a half years after Moscow’s full-scale invasion began.

The talks “present a viable chance to make progress as long as Putin takes action to prove he is serious about peace,” a Downing Street spokesperson said in a statement issued to reporters following the discussion.

Starmer and Zelenskyy praised Wednesday’s meetings between Trump and European leaders for showing a “powerful sense of unity and a strong resolve to achieve a just and lasting peace in Ukraine,” the spokesperson added.

Trump warned Wednesday that Russia would face “very severe consequences” if he believed Putin did not end the war, though did not specify what those would be. POLITICO reported Wednesday evening the U.S. president told European leaders he was willing to contribute security guarantees as long as the effort was not part of NATO.

Zelenskyy urged the U.K. to join NATO’s Prioritized Ukraine Requirements List (PURL) in a social media post following the meeting.

The Ukrainian president praised the “good, productive meeting” in the X post and said the pair discussed continuing support programs for Kyiv’s army and defense industry.

“Under any scenario, Ukraine will maintain its strength,” Zelenskyy posted. “Keir and I also talked about such mechanisms for weapons supplies as the PURL program, and I urged the U.K. to join.”

The PURL program was agreed during a meeting between NATO Secretary General Mark Rutte and Trump at the White House last month. Funded by European nations and Canada, the initiative will consist of regular payments of around $500 million to purchase equipment identified by Kyiv for its operational priorities.

The equipment and munitions would be sourced from U.S. stockpiles, with Germany, the Netherlands, Denmark, Norway and Sweden so far agreeing to take part.

Kyiv’s Defense Minister Denys Shmyhal tweeted Wednesday he’d spoken with Britain’s Defence Secretary John Healey about the forthcoming Ukraine Defense Contact Group meeting and Ukraine expects “the U.K .to play an important role” in PURL.

Zelenskyy said Ukraine plans to ratify a 100 year partnership agreement with the U.K. this month — a document which aims to further deepen security ties between the two countries. The Ukrainian president also pushed for investment to increase drone production which “can truly influence the situation at the strategic level.”

The Ministry of Defence did not respond to a request for comment.