The State Department said the US had obtained intelligence about the plan which involved staging a fabricated attack by the Ukrainian military either on Russian territory or against Russian speakers in eastern Ukraine.
In a statement, Foreign Secretary Liz Truss said such conduct was “completely unacceptable” and called on Russia to desist and return to the path of diplomacy.
“This is clear and shocking evidence of Russia’s unprovoked aggression and underhand activity to destabilise Ukraine,” she said.
“This bellicose intent towards a sovereign, democratic country is completely unacceptable and we condemn it in the strongest possible terms.
“The UK and our allies will continue to expose Russian subterfuge and propaganda and call it out for what it is. The only way forward is for Russia to de-escalate, desist and commit to a diplomatic pathway.”
State Department spokesman Ned Price said the US has intelligence on Russia's 'false flag' operation
The US said that Russia intended to use the video to accuse Kyiv of genocide against Ukraine’s Russian-speaking population.
It added that Russia would use the outrage that it created either to justify an attack or have separatist leaders in the Donbas region of eastern Ukraine invite a Russian intervention.
State Department spokesman Ned Price said the scheme included production of a propaganda video "with graphic scenes of false explosions depicting corpses, crisis actors pretending to be mourners and images of destroyed locations or military equipment entirely fabricated by Russian intelligence."
The US said the new intelligence indicates that the Russians would stage military equipment used by Ukraine, including a key weapon supplied by Turkey, a NATO member, to bolster the credibility of a fake attack. It has not provided detailed information backing up the claims.
The plan for a fake attack on Russian territory or Russian-speaking people was described in declassified intelligence shared with Ukrainian officials and European allies in recent days.
It was the latest example of the Biden administration divulging intelligence findings as a tactic to attempt to stop Russian disinformation efforts and foil what it says is Russian President Vladimir Putin’s effort to lay the groundwork for military action.
If Russia does invade, administration officials say they want to make clear Russia had always sought to create a pretext.
'Russia has signaled it's willing to continue diplomatic talks as a means to de-escalate. But actions such as these suggest otherwise.'
British officials indicated that having carried out their own analysis of the intelligence relating to the reports, they had “high confidence” Russia was planning to engineer a pretext for an invasion.
On a visit this week to show support for the government in Kyiv, Boris Johnson said there was “clear and present danger” of an attack and warned of punishing sanctions the moment the “first Russian toecap” stepped further into Ukrainian territory.
Last month the Foreign Office said that it had intelligence that Russia – which has an estimated 130,000 troops massed along its borders with Ukraine – was plotting to install a puppet government in Kyiv.