Keir Starmer has said Europe is “at a crossroads in history” and must act to support Ukraine to secure a lasting peace as he confirmed the UK and France would lead a “coalition of the willing” to help end the fighting.

After a crucial defence summit in London, Starmer said any plan for a lasting ceasefire would have to be “delivered together” with the US to provide a deterrence to Russia, as he continued attempts to repair frayed ties between Kyiv and Washington.

Starmer announced a deal that would allow Ukraine to use £1.6bn of export finance to buy more than 5,000 air defence missiles, to be made in Belfast and therefore creating jobs, as part of the government’s plan to boost economic growth.

The prime minister has spent the last 48 hours engaged in intense diplomacy after Volodymyr Zelenskyy and Donald Trump’s disastrous White House meeting on Friday, during which the Ukrainian president was berated live on camera by the US president and his deputy, JD Vance.

The defence summit, which brought together major European powers as well as Canada and Turkey, was intended to develop a united European response to the shift in the transatlantic consensus towards Ukraine but it took on a new urgency after the diplomatic clash.

Starmer said Britain and other European nations were willing to put “boots on the ground and planes in the air” to help provide an effective deterrent to Russia.

“It’s time to step up and lead and to unite around a new plan for a just and enduring peace,” he told reporters. “If you want to preserve the peace, you have to be prepared to defend the peace.”

Starmer said that to ensure Vladimir Putin did not breach any ceasefire with further attacks on Ukraine, there would have to be security guarantees from the US, with senior British officials saying that air, logistics and intelligence support would be necessary.

“To succeed, this effort must have strong US backing. We’re working with the US on this point after my meeting with President Trump last week. Let me be clear, we agree with the president on the urgent need for a durable peace. Now we need to deliver together,” Starmer said.

Trump has repeatedly resisted making any sort of military commitment to securing peace in Ukraine. Instead, he has suggested that an “economic backstop” of US civilians working on a multibillion-dollar critical minerals deal in the country would be sufficient.

At the defence summit, at Lancaster House in central London, the leaders agreed to keep military aid flowing to Ukraine, including after any ceasefire agreement, so that Kyiv would be in a strong position to deter any further attacks from Russia.

Other nations are also planning to raise their own defence budgets, after Starmer announced last week that the UK would increase military spending to 2.5% of GDP by 2027, with an ambition to hit 3% soon afterwards.

“Any deal must be backed by strength. Every nation must contribute to that in the best way that it can, bringing different capabilities and support to the table, but all taking responsibility to act, all stepping up their own share of the burden,” Starmer said.

The prime minister said that the leaders had also agreed to increase economic pressure on Russia.

The chancellor, Rachel Reeves, will sign a £2.3bn loan deal to allow Kyiv to buy more weapons, to be paid back using profits generated on Russian sovereign assets that are under sanctions.

She has also said she will change the remit of the £27.8bn national wealth fund so it could be spent on defence as well as infrastructure projects.

Leaving the summit, The European Commission president, Ursula von der Leyen, said that European leaders recognised they had to “urgently rearm” the continent, with the commission due to propose a plan on Thursday. “We need … to prepare for the worst, and [are] therefore stepping up the defences,” she said.

Mark Rutte, the Nato secretary general, said Europe was “stepping up” to make sure Ukraine could continue to defend itself if necessary, and had discussed what security guarantees they could provide, while following the UK by increasing their own defence budgets.

After the summit, Zelenskyy travelled to meet King Charles at Sandringham, with the offer of a royal audience interpreted at Westminster as a deliberate move to give the Ukrainian president equal treatment to Trump, who was last week presented by Starmer with an invitation to a second state visit to the UK.