The United States has accused Russia of planning to stage a "fake attack" to justify an invasion of Ukraine.
The Pentagon says it believes a "very graphic propaganda video" would feature as part of a campaign by Russia to "fabricate a pretext for an invasion".
Downing Street, meanwhile, says it has "high confidence" Russia is planning to fabricate a reason for incurring on Ukraine.
Pentagon Press Secretary John F. Kirby said: "We've discussed this idea of false flags by the Russians before.
"One option is the Russian government, we think, is planning to stage a fake attack by Ukrainian military or intelligence forces against Russian sovereign territory or against Russian-speaking people... to therefore justify their action.
"As part of this fake attack, we believe that Russia would produce a very graphic propaganda video, which would include corpses and actors that would be depicting mourners and images of destroyed locations, as well as military equipment, at the hands of Ukraine or the West."
Russia has denied being involved in false flag operations, while the US has not provided any further information to back up the claims.
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The Prime Minister's official spokesman said the UK had conducted its own analysis into the false flag claims and has "high confidence" Russia is planning to engineer a pretext for an invasion.
"We're considering options for further military deployments to support NATO's eastern flank, we're not at the stage of setting out details yet but we will come forward with those in due course," the spokesperson added.
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.