Boris Johnson has said there is a "diplomatic opening" in the Russia-Ukraine crisis but that intelligence was "still not encouraging" as he accused Vladimir Putin of sending "mixed signals".
Speaking after a COBR meeting, the Prime Minister said hopes of "deescalation" remained but said the Russian President was still amassing troops on the border of the eastern European country.
It comes as more than 130,000 Russian troops are said to have amassed at the border with Ukraine as fears mount Russian forces will launch a military assault.
“Last night going into today, clearly there are signs of a diplomatic opening," the PM said.
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.
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.
He 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.”
Earlier today, Foreign Secretary Liz Truss said a Russian invasion "would not stop at Ukraine" and could lead to conflicts in other countries.
The senior Tory said Europe was teetering "on the brink of war" and time was running out to find a diplomatic solution.
And she said the crisis could embolden other countries with military ambitions.
Ms Truss told Sky News: "If we saw an invasion into Ukraine, there would be severe costs in terms of a long-running conflict, we could see the undermining of security more broadly in Europe and could see other aggressors around the world see it as an opportunity to expand their ambitions too.
"This is a very dangerous moment for the world."
Meanwhile, Nato secretary-general Jens Stoltenberg has said there is cause for “cautious optimism” when it comes to quelling the crisis on the Ukrainian border.
Speaking at a press conference in Brussels, Mr Stoltenberg said there has so far been no signs of military de-escalation from Russia.
However, he said there appears to be a “willingness” from Moscow to “continue to engage in diplomatic efforts”.
“So far we have not seen any de-escalation on the ground – not seen any signs of reduced Russian military presence on the borders of Ukraine,” he said.
“But we will continue to monitor and to follow closely what Russia is doing. The signs coming from Moscow about a willingness to continue to engage in diplomatic efforts – that gives some reason for cautious optimism.
“We will, of course, follow very closely what’s happening on the ground and whether this is effected in some real de-escalation of the Russian military build-up in and around Ukraine.”
