Prime Minister Sir Keir Starmer will join a video call with European allies on Sunday ahead of Ukrainian President Volodymyr Zelensky’s visit to the White House next week.
French President Emmanuel Macron and German Chancellor Friedrich Merz will join Sir Keir in hosting the “coalition of the willing”, after Donald Trump and Vladimir Putin failed to reach a ceasefire deal at a summit in Alaska.
On Saturday, the prime minister praised Trump for having brought an end to the war in Ukraine “closer than ever before”, but warned that the “path to peace” could not be decided without Zelensky.
It comes after the US president said he wanted to bypass a ceasefire to move directly to a permanent peace deal.
On Saturday, the US president said on his Truth Social platform that it was “determined by all that the best way to end the horrific war between Russia and Ukraine is to go directly to a peace agreement”, in a major shift in position.
Zelensky later said that Russia’s refusal to agree to a ceasefire “complicates” efforts to end the war.
On Monday, the Ukrainian leader will travel to Washington DC, where US President Trump has said he will urge Zelensky to agree to a peace deal.
In the wake of the Anchorage summit, Sir Keir spent Saturday morning speaking to Western allies.
Following the calls, he said in a statement: “I welcome the openness of the United States, alongside Europe, to provide robust security guarantees to Ukraine as part of any deal.
“President Trump’s efforts have brought us closer than ever before to ending Russia’s illegal war in Ukraine.
“His leadership in pursuit of an end to the killing should be commended,” Sir Keir said.
Until Putin stops his “barbaric assault”, allies would “keep tightening the screws on his war machine with even more sanctions”, he added.
A Downing Street source told the BBC that any peace deal needed security agreements and “US involvement is a key part of that”.
Following a call with Trump on Saturday, Zelensky called for a lasting peace, “not just another pause between Russian invasions”.
He stressed Kyiv should be included in future discussions, and said he expected Russia to “increase pressure and strikes” in the coming days to “create more favourable circumstances for talks with global actors”.
On Friday, Zelensky visited Sir Keir at Downing Street, and the pair greeted each other in a warm embrace before holding talks over breakfast.
It was seen as a carefully co-ordinated show of support from the UK, ahead of the the Trump-Putin summit.
