Brits have been told to leave Ukraine immediately amid growing concerns of a possible Russian invasion.
The Foreign Office updated its advice on Friday evening to urge UK nationals to "leave now while commercial means are still available".
The warning came after Boris Johnson voiced fears for the security of Europe during a call with Western leaders including US President Joe Biden.
Defence Secretary Ben Wallace warned an invasion could come "at any time", with Russian President Vladimir Putin having amassed an estimated 130,000 troops on the border with Ukraine.
Mr Biden's national security adviser Jake Sullivan said there is the "credible prospect" of an invasion of some sort taking place before the end of the Winter Olympics on 20 February.
He said the Russians are in a position to "mount a major military operation in Ukraine any day now", which could include a "rapid assault on the city of Kyiv" or on other parts of the country.
Speaking from the White House, Mr Sullivan said Russia could choose "in very short order to commence a major military action against Ukraine" but stressed the US does not know whether Mr Putin has made a final decision.
The Foreign Office followed the US in advising against all travel to Ukraine, with a spokesman saying: "The safety and security of British nationals is our top priority, which is why we have updated our travel advice.
"We urge British nationals in Ukraine to leave now via commercial means while they remain available."
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