RUSSIA may rely on a blitzkrieg-style assault to storm its way across Ukraine before the West could react should Vladimir Putin decide to invade.
Fears of war have loomed once again in Eastern European as US officials warned their allies of a very real threat looming from Russia.
Britain's top general Nick Carter warned the chance of an "accidental" war with Russia is now the highest in decades.
And meanwhile Whitehall officials were described as being worried and twitchy about the troubling intel emerging from the East.
Russia has always insisted it means no harm to Ukraine - but the US have warned Putin to reconsider making a "serious mistake".
With tensions raging in Ukraine, Russian bombers flying over the North Sea, and Putin accused of stoking a migrant row between Belarus and Poland - the region sits on a knife edge.
Putin has long been accused of plotting to seize more territory from Ukraine after Russia illegally annexed Crimea in 2014.
But how would a Russian invasion of Ukraine actually play out?
According to one analysis, it would be a lightning strike similar to the Nazis storming across Western Europe in the early years of World War 2.
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Russia analyst Dr Mark Galeotti drew up the possible scenario in 2014 for .
And while the state of play has changed in the region over the past seven years, it still offers some insights into what Putin could do.
The expert describes the attack would be a "blitzkrieg" - the tactic made famous by Hitler's armoured divisions invading Belgium and France in 1940
Putin would seek to hit a knockout blow before Ukraine and the West could react and redraw the "frontline" - similar to what happened in Crimea.
Dr Galeotti explained Russia's aim would likely be not to conquer the whole country and the advance may only continue as far West as the port of Odessa.
Seizing the Black Sea port would cut Ukraine off from the coast and leave it landlocked - a key strategic win.
The patterns of Russian behaviour are different from what we have seen before
NATO Source
And key to the quick conquest would be using the pro-Russian forces already in Eastern Ukraine to cover their advance.
Russia would attempt to brand the seizure of the land as a "liberation"- much as they did with Crimea.
Special forces could be used to further build up support networks before the attack.
Putin has already accused of supplying and arming rebel groups fighting the disputed Donbas region between Ukraine and Russia.
Moscow would then seek to damage or totally cut off communications networks across the country before reaching "zero hour" - the time for invasion.
The first day of the Russian attack could be a massive operation which would see jamming, cyberattacks and sabotage unleashed on Ukraine's command structure.
With forces potentially cut off with central command, Russia would then unleash missiles, artillery and bombers to smash key infrastructure.
Bridges, airfields and train tracks would be bombed to try and stifle any chance of an effective Ukrainian counterattack.
And meanwhile, airports in eastern Ukraine would be seized by Spetsnaz commando forces, supporting by pro-Russian forces.
Paratroopers would then be dropped in to seize control of key cities.
They would then holdout until the arrival of core of the bulk of the Russian invasion army - which has been speculated to number around 100,000 troops.
"The aim, as mentioned, will be to move fast to seize and define a new front line wherever Moscow wants it," Dr Galeotti writes.
"They may well simply bypass Ukrainian troop concentrations when they can, leaving them to be mopped up later."
And should Putin's forces manage to not get bogged down - they could seize a huge swathe of Ukraine before anyone could stop them.
However, the expert noted the full-scale invasion makes "little real sense" as it could be spark action from the West.
But seven years on from his initial assessment, speculation has mounted that Putin may be seeking to test NATO's resolve - especially after the chaotic pullout from Afghanistan.
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All eyes are currently on Ukraine after the chilling warning from US officials was revealed - sparking concern across the West.
"The patterns of Russian behaviour are different from what we have seen before," a NATO source said.
"So far, it is unclear if this military build-up is intended to lead to an incursion into Ukraine or if it is just another exercise."
General Nick Carter, chief of the defence staff, told : "We’re in a much more competitive world than we were even ten or 15 years ago.
"We have to be careful that people don’t end up allowing the bellicose nature of some of our politics to end up in a position where escalation leads to miscalculation.
“Many of the traditional diplomatic tools and mechanisms that you and I grew up with in the Cold War, these are no longer there.
"And without those . . . there is a greater risk. That’s a real challenge we are confronted with.”
And when he was asked whether tensions with Russia and the risk of a war were greater now than at any stage in his 44-year career, Carter replied: "Yes".
He went on: "When you and I were growing up, it was a bipolar world.
"Two blocks, the Soviet Union and the West. We’re now into a period where it’s more multipolar.”
What is happening between Russia and Ukraine?
RUSSIA and the Ukraine have remained technically at war since 2014.
Ukraine was aligned with Russia as part of the Soviet Union until its collapse in 1991, following which it became an independent state.
Both nations remained closely tied - but Ukraine gradually began to distance itself, seeking deeper ties with the West.
The open conflict was triggered by the Ukrainian Revolution in 2014 - when an uprising overthrew the pro-Russian government of Viktor Yanukovych.
Vladimir Putin's forces reacted by annexing the region of Crimea from Ukraine - a move which was widely condemned by the West.
The conflict then spiralled when pro-Russian groups in Eastern Ukraine then took up arms against the state.
Russia gave their backing the separatist forces which formed breakaway republics in Donetsk and Luhansk.
Putin's forces then launched a military incursion into these regions as they gave their support to the rebels.
Russia continues to hold Crimea - and claims the region joined them willingly after they a referendum.
Seven years have now passed and the War in Donbass remains at a stalemate.
It is estimated some 14,000 have been killed in the conflict, including more than 3,0o0 civilians.
Ukraine and the rebels signed a new ceasefire in July 2020 - but clashes have been steadily increasing again throughout 2021.
Just last month, Russia staged massive "invasion" drills in Crimea with more than 40 warships and 30 jets in a terrifying show of strength.
US officials have now urged Moscow to reconsider making a "serious mistake", spurred by concerns from President Joe Biden.
But the Kremlin insisted it was not an aggressor and instead accused the US of goading Europe with its warnings.
Putin has already come under fire after being accused of creating a migrant crisis on the Poland-Belarus border to destabilise Europe.
The Kremlin previously warned the West was “playing with fire” by deploying warships in the Black Sea and warned of the “risks of a clash”.
They complained that two US warships and four NATO spy planes had
Earlier this week, US Secretary of State Antony Blinken reassured Ukraine that the US commitment to ensuring their security is "ironclad".
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Directly referring to the build up of Russian forces, he warned any "escalatory or aggressive actions would be of grave concern to the United States".
The West insists that under international law Crimea belongs to Ukraine.