Following a meeting of the Cobra emergency committee, Mr Johnson suggested there was a “diplomatic opening” to resolve the crisis without a war.
Russian President Vladimir Putin also said he was prepared for further talks with the US and Nato to ease tensions in eastern Europe.
What did Boris Johnson say?
Speaking to reporters in Downing Street, Mr Johnson said: “Last night going into today clearly there are signs of a diplomatic opening.”
But he added that the “intelligence that we are seeing today is still not encouraging”, with Russian field hospitals being built close to Belarus’s border with Ukraine.
However, the Prime Minister said the intelligence he had received was not encouraging, with the construction of field hospitals and the movement of extra forces closer to the border with Ukraine suggesting preparations were being made for an invasion.
But the Russians had the preparations in place to launch an invasion at “virtually any time”, he added.
He added that the “intelligence that we are seeing today is still not encouraging”, with Russian field hospitals being built close to Belarus’ border with Ukraine.
That could only be “construed as preparation for an invasion”, the Prime Minister said.
What did he say about the threat of an invasion of Ukraine?
Despite Russian claims about troop withdrawals, Mr Johnson said intelligence suggested “you have got more battalion tactical groups being brought closer to the border”.
“So, mixed signals, I think, at the moment,” Mr Johnson said.
Mr Johnson said there are “a lot of options” available to Russia if it were to choose to invade Ukraine.
Asked about suggestions from US intelligence that an invasion of Ukraine could occur in the early hours of Wednesday morning, the Prime Minister told broadcasters in Downing Street: “We think they have a huge preparation ready to go virtually at any moment.
“130,000 troops or more, a huge number of battalions – more than 90 battalions, tactical groups – and they are stationed around the Ukrainian border.
“Everyone can see what the potential routes in are – down to the south from Belarus, encircling the Ukrainian army in the east around the area, the enclave in Donbas or even coming up from the south from the sea, taking Odesa, Curzon.
“That’s the kind of thing they (could do). There a lot of options that they have.”
What has Vladimir Putin said?
Mr Putin, speaking following talks with German Chancellor Olaf Scholz in Moscow, said he was ready for negotiations with the US and the Nato alliance on limits for missile deployments and military transparency.
But he said Nato was rejecting Moscow’s demands to take membership of the alliance off the table for Ukraine and other former Soviet nations, halt weapons deployments near Russia’s borders and scale back force levels in eastern Europe.
Mr Putin said Russia did not want war, adding: “This is exactly why we put forward the proposal to start the negotiation process, where the result should be an agreement of ensuring equal security of everyone, including our country.
“Unfortunately there was no constructive response to this proposal.”
But he said there are still “elements that can be discussed”.
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