Western leaders have been on edge for weeks as they try to negotiate with Moscow, while more than 100,000 Russian troops stand ready at Ukraine’s border.
Vladimir Putin may well give them the green light in less than five days, German newspaper Der Spiegel reported.
The outlet cites information handed to intelligence services, including the Secret Service and the CIA, as its source.
The information is reportedly very detailed, down to the routes each attack will take.
US president Joe Biden is set to go into talks with Putin at 4pm UK time to try and resolve the crisis.
But multiple European nations, and the US, have been trying to deal with the conflict diplomatically for some time now – seemingly with no success.
The Kremlin previously said NATO was not listening to their security concerns about the alliance spreading too far eastwards.
Among other demands, Putin wants legally-binding reassurances that Ukraine will not be able to join NATO and then use its military power to take back Crimea – Ukrainian land Russia annexed in 2014.
He went as far as to threaten nuclear war if the territory was clawed back in this way.
But NATO leaders believe sovereign countries such as Ukraine have the right to choose their alliances without interference from world powers.
Tensions have only escalated since the start of the saga and things came to a head yesterday – when both the US and the UK told any citizens in Ukraine to leave.
The Foreign Office said last night: ‘The safety and security of British nationals is our top priority.
‘We urge British nationals in Ukraine to leave now via commercial means while they remain available.’