Prime Minister Boris Johnson has held talks in Kyiv with Ukraine's President Volodymyr Zelensky, Downing Street has said.
No 10 said the visit was a "show of solidarity" with the Ukrainian people.
A spokesman said Mr Johnson was using the trip to set out a new package of financial and military aid.
It comes the day after the UK announced £100m of weapons for Ukraine after the bombing of refugees at a railway station.
The spokesman said: "The prime minister has travelled to Ukraine to meet President Zelensky in person, in a show of solidarity with the Ukrainian people," he said.
"They will discuss the UK's long-term support to Ukraine and the PM will set out a new package of financial and military aid."
A photograph of the meeting was posted online by the Ukrainian embassy in London.
In a Facebook post, Andriy Sybiha, deputy head of the Ukrainian president's office, said: "The UK is the leader in defence support for Ukraine. The leader in the anti-war coalition. The leader in sanctions against the Russian aggressor."
Mr Johnson is the latest Western leader to travel to the Ukrainian capital for talks with the country's president.
European Commission President Ursula von der Leyen and the EU's foreign policy chief Josep Borrell both made visits on Friday, and Austrian Chancellor Karl Nehammer earlier on Saturday.
Earlier Mr Zelensky called on the international community to hold to account Russian forces who carried out the missile strike on Kramatorsk station, which was packed with women and children trying to flee the area.
The Kremlin has denied responsibility for the attack.
Speaking at a Downing Street press conference on Friday, Mr Johnson said the UK will send additional military equipment including Starstreak anti-aircraft missiles and 800 anti-tank missiles.
It followed an appeal from Ukraine for more arms as it prepares for an expected Russian offensive in the east of the country, after Moscow pulled back its forces from around Kyiv.
https://www.bbc.com/news/uk-61052643
