Sir Keir Starmer has said Europe and the US have warned Vladimir Putin that failure to agree to a 30-day ceasefire will result in “new and massive sanctions” and a significant increase in military aid to Ukraine.
The Prime Minister said Europe and the United States are “calling Putin out” to agree to a truce, following discussions with Donald Trump and the leaders of France, Germany, and Poland during his visit to Kyiv.
Starmer said that if the Russian leader is "serious" about peace then "he has a chance to show it now by extending the VE Day pause into a full, unconditional 30-day ceasefire".
"No more ifs and buts, no more conditions and delays,” he added.
The Prime Minister said Putin faces “massive sanctions” and increased military aid to Ukraine if he does not accept a 30-day ceasefire.
Trump has also promised "further sanctions" from the US if a truce, which has already been agreed by Ukraine, fails to start on Monday.
In a post on his Truth Socal platform on Thursday, he said that "if the ceasefire is not respected, the U.S. and its partners will impose further sanctions".
He added: "As President, I will stay committed to securing Peace between Russia and Ukraine, together with the Europeans, and a Lasting Peace it will be!"
In a remarkable turnaround just weeks after Trump’s tense Oval Office meeting with Ukrainian President Volodymyr Zelenskyy, Starmer said that the US and European leaders are now “speaking with one voice” on the crisis.
On Thursday, Sir Keir Starmer condemned the “hatred, tyranny and evil” of Putin’s war in Ukraine on the 80th anniversary of VE Day and spoke of modern parallels with the Second World War.
The Prime Minister paid tribute to the veterans of the Second World War who fought in the European theatre, as the UK marks 80 years since the Allies accepted the surrender of Nazi Germany.
Sir Keir and his Ukrainian, French, German and Polish counterparts spoke to US President Donald Trump on Saturday to update him on progress towards a peace deal.
The Prime Minister added: "Ukraine has shown the willingness to engage again and again, but again and again, Putin has refused.
"So we are clear, all five leaders here - all the leaders of the meeting we just had with the coalition of the willing - an unconditional ceasefire, rejecting Putin's conditions, and clear that if he turns his back on peace, we will respond.
"Working with President Trump, with all our partners, we will ramp up sanctions and increase our military aid for Ukraine's defence to pressure Russia back to the table."
Sir Keir has been in the Ukrainian capital with French President Emmanuel Macron, German Chancellor Friedrich Merz and Polish Prime Minister Donald Tusk for further talks on the so-called "coalition of the willing", with Ukrainian President Volodymyr Zelensky.
They also held a virtual meeting with other leaders involved in the coalition around the globe.
The five leaders in Ukraine on Saturday spoke to the US president on the phone, and are understood to have updated him on coalition of the willing plans, in a call that lasted about 20 minutes and was described by a UK source as "warm".
Mr Zelensky said on X that it was a "good conversation" with the American leader that was "positive and concrete".
"We share a common view: an immediate, full, and unconditional ceasefire is needed for at least 30 days. We propose it begin on Monday May 12. We are waiting for Russia's response," he said.
Sir Keir posted a video on X on Saturday to mark his visit to Kyiv, and said that he "will not rest until we secure a just and lasting peace for the Ukrainian people".
After arriving in Kyiv, Sir Keir, Mr Macron, Mr Tusk and Mr Merz joined Mr Zelensky and first lady Olena Zelenska to place candles at a makeshift memorial to killed Ukrainian soldiers, in Kyiv's Independence Square, during a ceremony marking the 80th anniversary of the end of the Second World War in Europe.
In a joint statement before their visit, Sir Keir, Mr Macron, Mr Tusk and Mr Merz said they "will stand in Kyiv in solidarity with Ukraine against Russia's barbaric and illegal full-scale invasion".
Military officers from about 30 countries have been involved in drawing up plans for the coalition of the willing which would provide a peacekeeping force in the event of a ceasefire being agreed between Russia and Ukraine.
