he Foreign Office on Friday urged all British nationals to leave Ukraine immediately as the US warned an invasion could take place “any day now”.
The Government issued its advice on Friday evening minutes before a White House press conference when US national security adviserJake Sullivan said an assault could begin during the Winter Olympics.
UK Defence Secretary Ben Wallace warned an invasion could come “at any time”, while Boris Johnson voiced fears for the security of Europe during a call with Western leaders.
Russian President Vladimir Putin has amassed an estimated 130,000 troops on the border with Ukraine – although he has denied he is planning an attack.
But Mr Sullivan said “the Russians are in the position to be able to mount a major military operation in Ukraine any day now.”
A Foreign Office spokesman said: “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.”
It also advised against all travel to Ukraine.
The US had earlier warned Americans in Ukraine that they should leave as he would not send troops on a rescue mission if Russia invades.
The number of Britons in Ukraine is understood to be in the low thousands.
Many of them are believed to live in the country, with some married to Ukranians, or with business interests, and so some of them may remain.
More staff may be withdrawn from the British Embassy in Kiev, though, an operational capacity will remain. Dozens of commercial flights a day are taking place between Ukraine and the UK. People can also leave the war-threatened country by road, including by crossing into Poland.
Mr Sullivan warned that a possible Russian invasion of Ukraine could come before the end of the Winter Olympics.The Games, taking place in China, finish in nine days time on February 20.
Speaking from the White House, he said: “We continue to see signs of Russian escalation including new forces arriving at the Ukrainian border.
“As we’ve said before, we are in the window of when an invasion begins at any time should Vladimir Putin decide to order it.
“I will not comment on the details of our intelligence information but I do want to be clear it could begin during the Olympics despite a lot of speculation that it will only happen after the Olympics.
“Any American in Ukraine should leave as soon as possible and in any event in the next 24 to 48 hours.”
It comes after US President Joe Biden warned on Thursday night “things could go crazy quickly” in Ukraine and urged American citizens to leave immediately.
Western leaders held a virtual meeting to discuss the crisis on Friday.
Mr Johnson told allies during the talks late on Friday afternoon that he fears for the security of Europe due to the situation in Ukraine, his office said.
A Downing Street spokesperson said: “The Prime Minister told the group that he feared for the security of Europe in the current circumstances.
“He impressed the need for Nato Allies to make it absolutely clear that there will be a heavy package of economic sanctions ready to go, should Russia make the devastating and destructive decision to invade Ukraine.
“The Prime Minister added that President Putin had to understand that there would be severe penalties that would be extremely damaging to Russia’s economy, and that Allies needed to continue with efforts to reinforce and support the Eastern frontiers of Nato. He urged the leaders to work together to deliver economic and defensive support to Ukraine.
“The leaders agreed that if President Putin deescalated, there was another way forward, and they pledged to redouble diplomatic efforts in the coming days.”
The meeting also included the leaders of the United States, Italy, Poland, Romania, France, Germany, the European Council, the European Commission and Nato.
Mr Wallace held talks in Moscow with Russian defence minister Sergei Shoigu as part of diplomatic efforts to avert war.
“Currently there’s over 130,000 troops stationed at readiness or exercising – plus warplanes, plus ships into the Black Sea – on the borders of Ukraine and that is an action that is not normal,” Mr Wallace told a news conference in the British embassy following the talks.
“It is beyond normal exercising therefore we will judge that statement on the evidence.”
Following a frosty meeting in Moscow on Thursday between Foreign Secretary Liz Truss and her counterpart Sergei Lavrov, Mr Wallace said his discussions with Mr Shoigui had been “frank and constructive”.
While he said that he took the minister’s assurances “seriously”, he admitted he was less optimistic than he had been previously that there could be a diplomatic solution to the crisis.
He said the current disposition of Russian forces meant they could do “a whole range of actions, including an invasion of a neighbouring country, at any time”.