LONDON — Britain, France and Ukraine have agreed to work on a ceasefire plan to present to the United States, British Prime Minister Keir Starmer said Sunday as he prepared to host a summit of European leaders.

The summit has been overshadowed by the extraordinary scolding US President Donald Trump gave Ukrainian President Volodymyr Zelensky at the White House on Friday for being ungrateful for US support in Ukraine’s battle against the invasion by Russia.

But Starmer said he is focused on being a bridge to restore peace talks and use the collapse of talks as an opportunity to re-engage with Trump and Zelensky and French President Emmanuel Macron rather than “ramp up the rhetoric.”

He told BBC news that an urgent round of calls to Trump, Zelensky and Macron over the weekend had cemented the idea that a “coalition of the willing” in Europe would need to move fast to come up with a peace plan to be presented to the United States.

That meant Europe moving faster than it has done to show it can defend itself, Starmer said, adding he was not criticizing other nations but making it clear that countries needed to step up as Britain and France had by offering peacekeeping troops.

“I am not criticizing anyone here, but rather than moving at the pace of every single country in Europe, which would in the end be quite a slow process, we’ve got to probably get to a coalition of the willing now,” he said.

“The UK and France are the most advanced on the thinking of this and that is why President Macron and I are working on this plan, which we will then discuss with the US,” he said, adding he did not think Zelensky had done anything wrong on Friday.

The London meeting has taken on greater importance in defending the war-torn ally and shoring up the continent’s defenses.

Sunday’s summit is likely to include talks on establishing a European military force to be sent to Ukraine to underpin a ceasefire. Starmer said it would involve “a coalition of the willing.”

Starmer said he does not trust Russian President Vladimir Putin but does trust Trump.

“Do I believe Donald Trump when he says he wants lasting peace? The answer to that is yes,” he said.

“There’s a real problem for European leaders to pick up the pieces and try and move forward,” Peter Ricketts, the former British national security adviser, said of the summit in an interview to BBC radio on Saturday. “It’s going to be a damage limitation exercise. It’s going to have to be an exercise in where do we go from here?”

The meeting at Lancaster House, a 200-year-old elegant mansion near Buckingham Palace, follows a charm offensive last week to engage with Trump at the White House to put Ukraine at the center of negotiations and tilt his allegiances toward Europe.

The summit will also include leaders from France, Germany, Denmark, Italy, Netherlands, Norway, Poland, Spain, Canada, Finland, Sweden, the Czech Republic and Romania. The Turkish foreign minister, NATO secretary-general and the presidents of the European Commission and European Council will also attend.

Zelensky received broad support from leaders across Europe after the White House fiasco, which was exceptional for featuring an attack on an ally — and because it was broadcast on live television.

Starmer embraced Zelensky when he arrived Saturday for a private meeting — a day before a get-together had been scheduled before the summit.

“As you heard from the cheers on the street outside, you have full backing across the United Kingdom,” Starmer said. “We stand with you, with Ukraine, for as long as it may take.”

Europe has been uneasy since Trump initiated direct peace talks with Russian President Vladimir Putin, who had been isolated by most Western leaders since invading Ukraine three years ago. The scramble to remain relevant and protect European interests as their once stalwart ally appeared to be cozying up to Putin was even more troubling when Trump called Zelensky a dictator and falsely said Ukraine started the war.

Meetings in recent days had provided some hope — until Zelensky’s visit to the White House.

Visits to the Oval Office by Macron, who had declared his visit a “turning point,” and Starmer were seen as steps in the right direction. The meetings were cordial and Trump even took a gentler tone toward Ukraine, though he would not commit to providing US security guarantees and maintained Europe would need to provide peacekeeping troops.

Within 12 hours of Starmer’s return from Washington, the talk of peace seemed to collapse as US Vice President JD Vance berated Zelensky for challenging Trump’s assertions that Russian President Vladimir Putin could be trusted.

“Starmer did an impressive job of asserting Europe’s agency in the war on Ukraine and conveying to President Trump that Europe is willing and able to take a leading role in implementing any credible peace deal,” said Rachel Ellehuus, director-general of Royal United Services Institute, a defense and security think tank. “Unfortunately, Friday’s White House meeting was a major step backward.”

Ukraine can no longer count on military or political support from the US after Trump declared himself neutral in negotiations, Ellehuus said. She said Europe needs to step in and could release some 200 billion euros ($207 billion) in seized Russian assets to help fund that effort.

“The immediate goal of the meetings in London must be to keep Ukraine in the fight so it can negotiate from a maximum position of strength,” she said.

Starmer pledged this week to boost military spending to 2.5 percent of gross domestic product by 2027. Other European nations may follow suit.

Czech Prime Minister Petr Fiala said Saturday that Europe faces a historic test and has to care for itself. He said European countries have to increase their arms spending to reach at least 3% of GDP.

“If we don’t increase our effort fast enough and let the aggressor dictate its conditions, we won’t end up well,” he said.

Macron, who said it was legitimate for the US to shift its focus to dealing with China and Asia, also called for more defense spending as he called for unity among his neighbors.

“We should have woken up earlier,” Macron said. “I’ve been saying for years that we need a more sovereign, more united, more independent Europe.”

Macron told Portuguese TV RTP in an interview he posted on X on Saturday that if Europe wanted to move towards “greater autonomy” in matters of defense and nuclear deterrence, its leaders should start a discussion about it.

“I am available to open this discussion…if it allows to build a European force,” he said. “There has always been a European dimension to France’s vital interests within its nuclear doctrine.”

French far-right leader Marine Le Pen was swift to react to Macron’s comments, saying at the Farm Show in Paris that “The French nuclear deterrent must remain a French nuclear deterrent…  It must not be shared, let alone delegated.”

French Defense Minister Sebastien Lecornu reiterated Macron’s stance that France’s vital interests include a “European dimension” adding that it was under the exclusive control of the French head of state.

“Our nuclear deterrent is French, and it will remain so: from the design and production of our weapons, to their implementation by decision of the President of the Republic,” he said on X.

“It protects the vital interests of France, which the head of state alone can define.”