UK nationals should leave Ukraine, the Foreign Office has said.

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.”

Prime Minister Boris Johnson spoke to world leaders on Friday including US President Joe Biden, French President Emmanuel Macron, German Chancellor Olaf Scholz and Nato secretary-general Jens Stoltenberg, as well as EU leaders Ursula von der Leyen and Charles Michel.

Mr Johnson told world leaders that he fears for the security of Europe, according to Downing Street.

The news comes after US president Joe Biden told American citizens to leave Ukraine following the threats of Russian military action where he warned that "things could go crazy quickly".

After a virtual call, a No 10 spokesman 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.”