Boris Johnson “fears for the security of Europe” as tensions mount over a potential Russian invasion of Ukraine and British people were urged to leave the country.

The UK prime minister voiced his concern during a call with Western leaders – including US president Joe Biden – as the Foreign Office updated its advice on Friday evening to urge UK nationals to “leave now while commercial means are still available”.

At the same time, 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 February 20.

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.

The warning was echoed by UK defence secretary Ben Wallace, who said warned an invasion could come “at any time”.

Tensions have heightened in the last 24 hours as Russian president Vladimir Putin has now amassed an estimated 130,000 troops on the border with Ukraine.

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.”

After Johnson and world leaders held the virtual call, a No 10 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.”

Speaking from the White House, 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 Putin has made a final decision.

Moscow denies it is planning an invasion and called the Western military actions provocations meant to bait Russia into war.

But diplomatic efforts to resolve the crisis have yet to yield results.