British Prime Minister Keir Starmer hosted a virtual meeting with world leaders from 25 countries on Saturday to bolster a so-called “Coalition of the Willing” against Russia in its ongoing conflict with Ukraine.

“We can’t allow President Putin to play games with President Trump’s deal,” said Starmer from 10 Downing Street in London.

Leaders representing Ukraine, the European Union (EU) Commission, North Atlantic Treaty Organisation (NATO), Canada, Australia and New Zealand were expected to have joined the meeting to discuss the peace deal being negotiated by US President Donald Trump.

The call comes ahead of a military planning session next week when these countries will decide on the nature of troop deployments to support peace in the region.

“If Putin is serious about peace, it’s very simple: he has to stop his barbaric attacks on Ukraine and agree to a ceasefire; and the world is watching,” he said.

Starmer accused the Russian administration at the Kremlin of a “complete disregard” for Trump’s 30-day ceasefire proposal.

“It only serves to demonstrate that [Russian President] Putin is not serious about peace. If Russia finally comes to the table, then we must be ready to monitor a ceasefire to ensure it is a serious, and enduring peace; if they don’t, then we need to strain every sinew to ramp up economic pressure on Russia to secure an end to this war,” he said.

Starmer accused Putin of trying to delay matters by calling for a “painstaking study” before a ceasefire can take place.

“But the world needs to see action, not a study or empty words and pointless conditions. My message to the Kremlin could not be clearer: stop the barbaric attacks on Ukraine, once and for all, and agree to a ceasefire now. Until then we will keep working around the clock to deliver peace,” he added.

The UK believes countries need to ratchet up economic pressure on Russia to force Putin into negotiations in the short term and be prepared to support a “just and enduring peace in Ukraine” over the long term.

It also wants to continue to “ramp up” military support for Ukraine to enable Kyiv to defend itself against Russia.

As part of a three-point agenda, Starmer called on the world leaders to keep strengthening Ukraine, be prepared to defend any deal through a Coalition of the Willing, and keep up the pressure on Russia.

According to Downing Street, Saturday’s call follows a week of "intensive diplomacy" by UK ministers after Defence Secretary John Healey travelled to Paris to meet counterparts from Germany, France, Poland and Italy, and the Foreign Secretary travelled to Canada for G7 Foreign Ministers.

The UK government has indicated that Britain could send peacekeepers to Ukraine in the event of a ceasefire deal, but has called Washington to offer a security “backstop” to those forces.

It comes after Ukraine backed the American proposal for a 30-day ceasefire, but Putin said that "lots of questions" remain over that proposal.

Moscow has reportedly also presented a "list of demands" to the US to end the war.