A host of countries have urged their nationals to leave Ukraine, amid growing warnings of a Russian invasion.
The British foreign office said all UK nationals “should leave now while commercial means are still available”.
Nato Secretary-General Jens Stoltenberg said the bloc was “united and prepared for any scenario”, while the US warned Russia could attack “at any time”.
Russia has repeatedly denied any plans to invade Ukraine despite massing more than 100,000 troops near the border.
US Secretary of State Antony Blinken said new Russian forces had arrived at the border in what he described as “very troubling signs of Russian escalation.”
Moscow has just begun massive military drills with neighbouring Belarus, and Ukraine has accused Russia of blocking its access to the sea.
The Kremlin says it wants to enforce “red lines” to make sure that its former Soviet neighbour does not join Nato.
We’re in a window when an invasion could begin at any time, and to be clear, that includes during the Olympics [which end on 20 February],” Mr Blinken said.
US national security advisor Jake Sullivan said Russian forces were “in a position to be able to mount a major military action at any time” and urged American citizens in Ukraine to “leave as soon as possible” in remarks seen as a clear escalation in the urgency of warnings from US officials.
“We obviously cannot predict the future, we don’t know exactly what is going to happen, but the risk is now high enough and the threat is now immediate enough that [leaving] is prudent,” he added.
President Biden has said that he would not send any troops to rescue any citizens left stranded in the event of Russian action.
Among other countries calling on citizens to leave are the Netherlands, Japan and South Korea. In its warning Latvia cited “a serious threat to security posed by Russia”.
Meanwhile, diplomatic efforts are underway to defuse the current crisis.
UK Defence Secretary Ben Wallace warned his counterpart in Moscow that a Russian invasion of Ukraine would have “tragic consequences” for both countries. But Sergei Shogiu said growing military tensions in Europe were “not our fault”.
The current tensions come eight years after Russia annexed Ukraine’s southern Crimea peninsula. Since then, Ukraine’s military has been locked in a war with Russian-backed rebels in eastern areas near Russia’s borders.
Credit: BBC