Prime Minister Boris Johnson met with Ukrainian President Volodymyr Zelensky in Kyiv.
The visit was described by No 10 as a "display of solidarity" with the Ukrainian people.
Following the discussion, Downing Street announced that the United Kingdom will send 120 armored vehicles and anti-ship missile systems to Ukraine to assist the country.
Senior members of Mr Zelensky's team hailed the United Kingdom for its assistance during the dispute with Russia.
Mr Johnson's travel to Kyiv was not publicised in advance, and the Ukrainian embassy in London posted a photo of his meeting with President Zelensky on Twitter as the first clue that he was in the city.