Some British Embassy staff and their families are being withdrawn from Ukraine as the threat from Russia mounts.
The Foreign Office confirmed that some officials were being pulled out of Kyiv after the United States ordered the families of American embassy staff to leave the country.
Russian troops have gathered on the border with Ukraine, with fears mounting of a military attack.
The FCDO guidance said: "Some Embassy staff and dependants are being withdrawn from Kyiv in response to growing threat from Russia.
"The British Embassy remains open and will continue to carry out essential work."
Brits are advised against all travel to Donetsk oblast, Luhansk oblast and Crimea, and all but essential travel to the rest of Ukraine.
Deputy PM Dominic Raab warned on Sunday that there was a "very significant risk" Russia would mount an invasion of Ukraine.
Asked about the threat of an invasion, he told the BBC: "I think there is a very significant risk of it.
"The world needs to keep its eye on this and be very clear with President Putin that it would not do this cost-free, that there would be a price.
"A price in terms of the strenuous defence that we would expect the Ukrainians to put up, but also the economic cost through sanctions, which are of course more effective if the international community speaks as one or at least with a broad consensus."
Foreign Secretary Liz Truss accused the Russians of plotting to undermine the Ukrainian government in Kyiv.
"The information being released today shines a light on the extent of Russian activity designed to subvert Ukraine, and is an insight into Kremlin thinking," she said.
"Russia must de-escalate, end its campaigns of aggression and disinformation, and pursue a path of diplomacy.
"As the UK and our partners have said repeatedly, any Russian military incursion into Ukraine would be a massive strategic mistake with severe costs."
Russia's Foreign Minister accused the UK of circulating "disinformation" - and told the Foreign Office to "cease these provocative activities" and "stop spreading nonsense".
Vadym Prystaiko, Ukraine's ambassador to the UK, said a Russian invasion is "very likely" but said that "there is still room for diplomatic resolution".
Mr Prystaiko said Ukraine is "prepared to fight" but said the country is not well-equipped for lengthy conflict.
