The Ukrainian president has met the King at Windsor Castle ahead of talks with the prime minister.
Volodymyr Zelenskyy is meeting Sir Keir Starmer to discuss his country’s defences and new ways to increase pressure on Russia.
Mr Zelenskyy also met Commons Speaker Sir Lindsay Hoyle during a visit to parliament on Monday afternoon before going to Downing Street.
He and Sir Keir embraced on the doorstep of No 10, where a red carpet had been rolled out for the Ukrainian leader.
The visit to London comes ahead of a two-day summit of NATO leaders in The Hague, with increased defence spending top of the agenda.
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Mr Zelenskyy has been invited to the summit, but will not take part in its main discussions. It is still unclear whether he will attend.
On Monday, he looked relaxed in pictures of his meeting with the King, which was followed by lunch.
As they made their way through the royal residence, they were pictured chatting and smiling.
The King and the Ukrainian leader have met numerous times.
In March, they met at Sandringham in Norfolk just days after Mr Zelenskyy’s bruising encounter with Donald Trump in the Oval Office.
At the time, the Ukrainian leader spoke of how grateful he was for the King’s support.
They also met last July at the European Political Community summit at Blenheim Palace in Oxfordshire.
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Mr Zelenskyy’s visit to the UK follows reports that Russia fired 352 drones and 16 missiles at Ukraine overnight, killing at least 10 civilians, including seven in Kyiv.
He said preliminary reports indicated Russia had used North Korean missiles to attack Kyiv and described those two countries, and Iran, as a “coalition of murderers”.
