Russia will launch a full-scale invasion of Ukraine complete with airstrikes and a 200,000- soldier ground attack within the next 48 hours, US intelligence claims.
Pentagon sources have warned Kyiv that Vladimir Putin is fully prepared to send the huge military presence amassed at the border into Ukrainian territory - and that he's "highly likely" to take this option.
Speaking to Newsweek, one US defence official said: "The President of Ukraine has been warned Russia will highly likely begin an invasion within 48 hours based on US intelligence."
The official believes Moscow may have already violated its former ally's airspace, by "flying possible reconnaissance aircraft for a short period" earlier today.
A Ukrainian source confirmed receipt of the warning from American allies.
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But they noted Kyiv has been told three times of a looming large-scale invasion in the past month.
The source told Newsweek: "It's possible for sure.
"Putin can't keep so many troops in the field much longer."
There are close to 200,000 war-ready Russian troops gathered at the border and they are as prepared for battle as they can be, another US defence official told Reuters.
Eighty per cent of the infantry units, artillery, tanks and other weapons of war are in forward positions, they said.
And almost 100 per cent of the forces the Pentagon expected to be assembled for an invasion have gathered, the official added.
The Pentagon's vision of a large-scale invasion includes airstrikes, cruise missiles and troops marching into Ukrainian territory.
A second US official detailed just how comprehensive the Russian invasion plans are as they confirmed the same 48-hour timeline, Newsweek reports.
According to the second source, forces are set to swarm further than the rebel held pro-Moscow territories of Donetsk and Luhansk - where Putin has already deployed troops as "peacekeepers".
Invading forces are expected to enter through the northern border with Belarus - a close Moscow ally - sweeping down towards the capital, Kyiv, the second official explained.
They claim the all-out thrust into Ukrainian territory will start with a cyber attack followed by a nocturnal ground invasion.
Following the Newsweek report, a number of Ukrainian government websites were down, signalling the attack may have already begun.
A third US source said the White House has become "incredibly pessimistic" that the Kremlin will limit aggression to the two rebel-held republics.
They also confirmed a 24-48-hour timescale for the grand invasion plan.
Adding to the growing evidence of a looming bombardment, a NATO military official told CNN that allies are being briefed on the same intelligence.
However, the official warned "no one knows for sure" what Putin is planning, echoing other officials who say plans could change depending on daily developments.
British Defence Secretary Ben Wallace reiterated concerns of Putin's unpredictability, claiming the Russian president has gone "full tonto" over the crisis.
Dishing out fighting talk, Wallace claimed the UK can kick Russia's "backside" as he revealed the UK will "shortly" send a new package of highly sophisticated defensive weapons to its eastern European ally.
Wallace' also revealed the broadcast licence for Russian "propaganda" channel RT is now under review.
Boris Johnson announced sanctions on five banks and three oligarchs yesterday after Putin said he would send troops into two breakaway regions.
But the sanctions were branded not strong enough by MPs across the House of Commons as the three billionaires were already sanctioned by the US.
Chelsea FC owner Roman Abramovich was not targeted despite Boris Johnson wrongly suggesting otherwise.
Mr Wallace's unguarded comments came during a chat with military personnel at the Horse Guards building in Westminster. He compared the Russian president to Tsar Nicholas I during the Crimean War as he "had no friend, no alliances".
The former Scots Guards officer added his regiment had "kicked the backside" of the Tsar in the Crimea and "we can always do it again".
Mr Wallace said: "It's going to be a busy Army. Unfortunately we've got a busy adversary now in Putin, who has gone full tonto."
