The US has warned of the “very distinct possibility” of a Russian invasion of Ukraine in the next few days, potentially involving an overwhelming attack on Kyiv, and told all remaining Americans to leave the country in the next 48 hours.

Diplomatic sources said that Joe Biden had told allies leaders in a call that Vladimir Putin had taken a decision to go ahead with an invasion, but Jake Sullivan, the national security adviser, said that the US did not believe the Putin had given “a final go order”.

“I will say that the way that he has built up his forces and put them in place, along with the other indicators that we have collected through intelligence, makes it clear to us that there is a very distinct possibility that Russia will choose to act militarily, and there is reason to believe that that could happen on a reasonably swift timeframe,” Sullivan said.