Keir Starmer accused Vladimir Putin of dragging his feet over agreeing to a ceasefire with Ukraine on Saturday as international pressure grew on the Russian president to enter talks.
The prime minister said there was a limit to the length of time Putin could prevaricate, after he convened a virtual summit with 29 other international leaders who agreed to take plans for a peacekeeping force to an “operational phase”.
Starmer said military chiefs would meet in London on Thursday to “put strong and robust plans in place to swing in behind a peace deal and guarantee Ukraine’s future security”.
Those who took part in the virtual summit included the French president, Emmanuel Macron, and the Ukrainian president, Volodymyr Zelenskyy.
Afterwards, Starmer said “new commitments” had been made on both peacekeeping and tightening sanctions on Russia.
“Sooner or later, he is going to have to come to the table and engage in serious discussions,” the prime minister said.
“So this is the moment: let the guns fall silent, let the barbaric attacks on Ukraine once and for all stop, and agree to a ceasefire now.”
As well as the European nations, the leaders of Australia, Canada and New Zealand also joined the call, as did Nato’s secretary general, Mark Rutte.
Saturday’s meeting followed an intense week of diplomacy in which American and Ukrainian officials agreed on a proposal for an unconditional 30-day ceasefire, which was put to Russia.
But the Kremlin has so far resisted the deal, saying it would only agree to a ceasefire if Ukraine also agreed to abandon its aim of joining Nato and gave up some of its territory to Russia.
In Kyiv, Zelenskyy said Russia was playing for time so it could get into a stronger military position before any ceasefire.

“I think the delaying of the process is exactly because of what I said. They want to improve their situation on the battlefield,” Zelenskyy told a group of journalists in a briefing at the presidential administration.
He said Ukraine had shown its willingness to agree to US proposals for a temporary ceasefire during which terms for a more lasting deal could be discussed, as agreed last week at talks in Saudi Arabia.
“Today, Putin is the one who doesn’t agree with what [Donald] Trump has proposed,” he said.
Zelenskyy said Russia’s attempts to impose conditions on a ceasefire should be rejected out of hand.
“This is a ceasefire for 30 days; it’s not for ever, it’s 30 days, during which all sides have the chance to demonstrate their willingness to end the war,” he said.
Although it is clear that any potential agreement would probably require Ukraine to accept de facto Russian control of some Ukrainian land, he ruled out formally ceding any territory to Russia.
“Our position is that we do not recognise the occupied Ukrainian territories as Russian in any case,” he said. Zelenskyy called the territorial issue complex and said it should be “resolved later, at the negotiating table”.
Writing in the Observer, the UK foreign secretary, David Lammy, also taunted Putin, saying he had been put on the spot by Ukraine’s agreement to a ceasefire and the moves, led by the US president, Donald Trump, to end the conflict.
“The proposal for a ceasefire is therefore a test. He can’t simply say he is ready to end this war – he has to prove it.”
Lammy, who attended a meeting of G7 foreign ministers in Canada last week, said the group of nations known as the “coalition of the willing” was determined to create the conditions “that guarantee that Russia does not come back for more”.
Referring to the security guarantee that these nations plan to offer, Lammy added: “To be credible, it needs US support. But Britain and our allies recognise that the bulk of the contribution must come from Europeans.”
Asked about whether he discussed seizing Russian assets with his counterparts, Starmer said it had been on the agenda but added it was “a complicated question”.
Meanwhile, both Russia and Ukraine launched drone attacks overnight, each reporting more than 100 enemy drones entering their respective airspaces.