The German Olaf Scholz, the Polish Andrzej Duda and the Italian Mario Draghi were also in the game, as well as the head of NATO. It comes as Russia has stationed around 100,000 troops on its border with Ukraine. In response, 8,500 US troops were placed on heightened alert for possible deployment to Eastern Europe, the Pentagon said.
Forces could be sent at short notice to support NATO troops, should the bloc activate a rapid reaction force.
Mr Johnson had previously warned of “dark” intelligence suggesting Russia was planning a raid on Kiev.
But Pentagon spokesman John Kirby said he had not yet made a decision on whether or not to deploy the troops.
NATO has so far stationed around 4,000 troops in Estonia, Lithuania, Latvia and Poland.
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He said that, “from the Russian point of view”, any invasion “is going to be a painful, violent and bloody affair”.
He added: “I think it is very important that people in Russia understand that this could be a new Chechnya.”
“I have to tell you that I think the intelligence is pretty dark at this point.
“There is certainly a very, very wide range of Russian forces and we have to take the necessary measures.
“I don’t think it’s inevitable now, I think that sense can still prevail.”
Speaking of the Ukrainian people, he said: “My judgment is that they will fight.”
Downing Street confirmed that there were “no plans to send British combat troops” to Ukraine.
Meanwhile, the Foreign Ministry announced it was withdrawing some embassy staff from the country’s capital.
A spokesperson said: “Some embassy staff and dependents are being withdrawn from Kyiv in response to the growing threat from Russia.
“The British Embassy remains open and will continue to carry out essential work.”
A spokesman for the prime minister said around 30 British diplomats, including the ambassador, remained in the country.