BORIS Johnson has warned that Russia is planning the "biggest war in Europe since 1945" as Putin intends to "invade and encircle Kyiv."
It comes as the world waits with bated breath to see what Russia will do next - after signs show that plans to invade Ukraine have "already begun."
Asked if he believes a Russian invasion is imminent, Mr Johnson told the BBC: "I'm afraid that that is what the evidence points to, there's no burnishing it.
"The fact is that all the signs are that the plan has already, in some senses, begun."
The PM also warned Putin that he faces decades of "bloodshed and misery" if his troops invade Ukraine.
It comes amid reports of explosions rocking Donetsk on Saturday night - after 1,500 ceasefire violations were reported in east Ukraine in one day alone.
Putin is feared to be massing a force of up to 200,000 soldiers, supported by tanks, artillery and armoured vehicles on the edge of the former Soviet state.
Russia and Ukraine have been at loggerheads ever since Kyiv began to grow closer to the West - leading Russia to annexing Crimea in 2014 and stoking separatists to take up arms in the Donbas in eastern Ukraine.
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And NATO chief Jens Stoltenberg said: "Every indication indicates that Russia is planning a full-fledged attack against Ukraine.
"We all agree that the risk of an attack is very high."
Yesterday, Mr Johnson told world leaders that an invasion of Ukraine by Russia is now looking "increasingly likely" according to intelligence - and later said the attack appears to already be "in motion".
"If Ukraine is invaded, the shock will echo around the world," said the PM in a chilling warning during his speech at the Munich Security Conference.
Asked whether he agreed with the US assessment that the Russian leader had made up his mind to attack the capital city Kyiv, he told broadcasters: "I think certainly things are in motion.
"But the question is whether it can all be pulled back, and whether the president of Russia is still able to call this operation off."
He added: "Imagine the invasion of Ukraine, a country of 45 million people, the second biggest country in Europe geographically apart from Russia itself - an absolutely colossal place.
"You can't hold it down. There will be a protracted, violent, bloody insurgency with the loss of life for young Russians, as well as for Ukrainians."
Boris insisted there is still time for a diplomatic solution, and said an invasion would be a "crazy, disastrous venture" for Russia.
SHOCK & AWE
And all eyes are now are now on the relatively small region, which is currently under the control of two pro-Russian rebel groups, the Donetsk People's Republic (DPR) and the Luhansk People's Republic (LPR).
Shelling has been reported across the region as Ukraine, Russia and the separatists point fingers at each other over the clashes.
There have been reports of artillery shells falling within Russia's borders, at least two of Ukrainian soldiers being killed, and loud explosions heard throughout the Donbas.
Both separatist groups ordered mass evacuations yesterday as they accused Ukraine of planning a wide scale attack - including alleging Kyiv was going to blow up a chemical plant.
And now both have also declared the "full mobilisation" of their military forces.
Flurries of violence have since been reported with at least one car bomb being detonated in the city of Donetsk.
It comes as:
- Vladimir Putin oversaw nuclear and hypersonic weapons drills amid the tensions
- Boris Johnson warned Vladimir Putin will "pile the coffins high" with war in Ukraine
- It was warned the UK is fighting with "one hand tied" against a resurgent Russia and China
- Huge explosions were heard in eastern Ukraine overnight amid fears of imminent invasion
- Britain has moved its embassy in Kyiv some 336 miles away as the tensions rage
- Pro-Russian rebels ordered an evacuation from the Donbas - accusing Ukraine of planning an attack
The West has "got to hope and believe" that Vladimir Putin can still be dealt with rationally, Boris said.
And he warned violence from Moscow against Ukraine will "truly test" Nato but stopped short of saying alliance forces should directly intervene.
He warned an attack by Putin would bring about the "destruction of a democratic state".
The PM also pledged more sanctions on Russia if Putin invades and pledged to take down Russian money in London.
Ukrainian president Volodymyr Zelensky also met with Boris, and himself gave a speech - calling on NATO members to be honest about whether they wanted Kyiv to join the alliance.
The 44-year-old leader received a standing ovation before starting remarks in which he called on the world to learn the "terrible lessons from history" and chided the international community for what he said was the appeasing of Russia.
"The rules that the world agreed on decades ago no longer work. They do not keep up with new threats. Not effective for overcoming them. This is a cough syrup when you need a coronavirus vaccine," he said.
Elsewhere, US President Biden said he is convinced that Putin has decided to invade Ukraine.
Biden said that the invasion would come in the next week or days - but left the door open for a diplomatic resolution.
"Russia has a choice between war and all the suffering it will bring or diplomacy that will make a future for everyone," Biden said at the White House Friday.
The United States said that with an estimated 149,000 Russian troops on Ukraine's borders - as many as 190,000, when including the Russian-backed separatist forces - an attack is inevitable.
The Russians have never given a figure for the deployment along the border with Ukraine nor how many are taking part in ongoing drills with neighbouring Belarus.
Compounding fears, Putin personally oversaw previously scheduled drills involving missile launches on Saturday.
"He's focussed on trying to convince the world he has the ability to change the dynamics in Europe in a way that he cannot," Biden added.
It is feared that Putin could use the rising chaos in the Donbas as pretext to move in his troops.
Western intelligence officials have repeatedly suggested that Vlad could use a "false flag" - a staged attack or threat to give them an excuse to invade.
Russia has also been stoking accusations of "genocide", with Russia’s foreign ministry spokeswoman Maria Zakharova claiming that life in the Donbas is “hell” for ethnic Russians.
Meanwhile, Putin has signed a decree to call up tens of thousands of army and secret service reservists.
Kyiv denied accusations by the rebel groups that they were planning an imminent attack on the Donbas.
The Ukrainian military said on Saturday it had recorded 12 ceasefire violations by pro-Russian separatists in eastern Ukraine in the morning after 66 cases in the previous 24 hours.
Separatist authorities also reported what they said was shelling by Ukrainian forces of several villages on Saturday.
Both sides regularly trade blame for ceasefire violations.
Officials told local media that 25,000 people had left Lugansk and more than 6,000 had left Donetsk for Russia. There were reports of long car queues at checkpoints in Donetsk.
NATO chief Stoltenberg warned the size of the assembled Russian force far exceeded that needed for military drills, and that Russia had the capacity to invade without warning.
France and Germany have urged Russia to use its influence on rebels in Ukraine's disputed east to "encourage restraint and contribute to de-escalation".
But on the ground, a spike in clashes has fed a powerful sense of dread.
Monitors from the Organization for Security and Co-operation in Europe said Saturday they had seen a significant rise in the number of attacks along the front line, particularly in the separatist areas of Donetsk and Lugansk.
Seeking to reverse the aggressor narrative, Moscow-backed leaders have accused Kyiv of planning an offensive to retake the eastern territories. The evacuations of civilians there were said to be in response to worries about a government attack.
Russian news agencies quoted officials in Lugansk saying there had been two explosions within an hour on a gas pipeline but the fires were under control.
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But US Secretary of State Antony Blinken, who will meet his Russian counterpart for talks Thursday according to Biden, accused the Kremlin of mounting a propaganda campaign to create an excuse for war.
Biden again ruled out sending US troops into Ukraine, but his administration reiterated that it would hit Moscow with costly sanctions that would transform Russia into "a pariah to the international community".