Starmer and Zelensky meet at Downing Street
Jonathan Brady / PAPrime Minister Sir Keir Starmer and Ukrainian President Volodymyr Zelensky embraced outside Downing Street as the pair met for key talks at No 10.
Zelensky arrived in the UK earlier on Saturday, in the wake of a White House meeting with US President Donald Trump that descended into a row between the two leaders over the war in Ukraine.
On Sunday, Sir Keir will host a summit of European leaders to discuss bringing the war Russia-Ukraine war to an end and wider European defence - while Zelensky is expected to meet King Charles III at the request of the UK government.
The meetings will now be overshadowed by recent events in Washington and concerns about a hardening of relations with the US.
In recent weeks, the prime minister sought to cast himself as a bridge between the US and Europe as it adapts to the Trump administration's desire to be less involved in European defence, having a cordial meeting with Trump a day before Zelensky's.
During that meeting, he hand-delivered a letter from King Charles inviting Trump - who is fond of the Royal Family - to an unprecedented second state visit, which SNP MPs called on the PM to withdraw following the Oval Office spat.
Sir Keir has also attempted to be a conduit for Ukraine as it seeks security guarantees in any peace deal - contacting both Trump and Zelensky by phone in the aftermath of their row.
Following the acrimonious White House meeting, Zelensky has attempted to paper over the cracks.
In a statement, he said of Trump: "Despite the tough dialogue, we remain strategic partners. But we need to be honest and direct with each other to truly understand our shared goals."
When his plane landed in the UK, the Ukrainian leader wrote in a string of social media posts: "It's crucial for us to have President Trump's support. He wants to end the war, but no one wants peace more than we do.
"We are the ones living this war in Ukraine. It's a fight for our freedom, for our very survival."
Sunday's summit in London is the latest round of top-level European meetings in response to Washington's new approach to ending the war in Ukraine, which began with Russia's full-scale invasion over three years ago.
The Trump administration has so far excluded Europe from preliminary talks with Russia, while the president has been accused of parroting Russian propaganda.
Top of the agenda on Sunday will be increasing Europe's defence capabilities as the US steps back, as well as seeking security guarantees for Ukraine from the White House as part of any peace deal.
Ahead of the last summit in Paris, Sir Keir proposed deploying British troops to Ukraine as part of a European peacekeeping force - but said this would require a US security "backstop".
Trump has consistently resisted to fully committing direct US military support to a Ukraine peace deal, but has offered closer economic ties including a minerals deal, which he said could act as a deterrent.
And since Friday's furious row, media reports from the US suggest Trump is considering cutting off aid to Ukraine altogether.
At the same time, European leaders have recognised the need to increase defence spending - but experts have warned that the UK's military was currently unready to meet an enlarged defence role.
More than a dozen leaders are due to meet with Sir Keir and Zelensky on Sunday, including outgoing German Chancellor Olaf Scholz, Polish President Donald Tusk, French President Emmanuel Macron, European Commission President Ursula von der Leyen, Nato Secretary-General Mark Rutte, and the European Council President António Costa.
A special European Commission defence package will be announced on 6 March, according to Tusk.
The Oval Office spat prompted European allies to mount a spirited defence of the embattled Ukrainian president.
On Saturday, the European Union's top diplomat, Kaja Kallas, warned that it had "become clear that the free world needs a new leader. It is up to us, Europeans, to take this challenge."
Friedrich Merz, who is expected to become Germany's next chancellor, wrote that he stood with Ukraine "in good and testing times", adding: "We must never confuse aggressor and victim in this terrible war."
While diplomatic efforts to bring the war to a close continue, fighting rages on.
Seven people were injured in an overnight drone attack on the north-eastern city of Kharkiv.
Ukraine's state emergency service said 64 people - most of them patients - were evacuated from a three-storey medical facility that caught fire after being hit by one of the drones.
In Russia, the country's defence ministry reported that 48 Ukrainian drones had been "intercepted and destroyed" overnight in eight regions, including in Crimean peninsula, which was annexed by Russia in 2014.