The foreign secretary tweeted: "This is clear and shocking evidence of Russia's unprovoked aggression and underhand activity to destabilise Ukraine.

"This bellicose intent towards a sovereign democratic country is completely unacceptable and we condemn it in the strongest possible terms."

Government officials in America outlined how their intelligence indicated Russia was planning to use corpses and actors in order to create a propaganda video to provide them with a cause to attack.

Pentagon spokesman John Kirby said: "We've discussed this idea of false flags by the Russians before - we've made no secret of that. And we do have information that the Russians are likely to want to fabricate a pretext for an invasion, which again, is right out of their playbook.

"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."

State Department spokesman Ned Price said the US is making the information public to show Russia's destabilisation attempts in the region.

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In response to claims reported by The New York Times and The Washington Post, US deputy national security adviser Jonathan Finer said: "We don't know definitively that this is the route they (Russia) are going to take.

"But we know that this is an option under consideration - that would involve actors playing mourners for people who are killed in an event that they (Russia) would have created themselves."

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Mr Kirby added: "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 - even to the point where some of this equipment would be made to look like it was Western supplied into Ukraine equipment."

The plan is one of the options Russian leader Vladimir Putin is considering, according to the State Department.

It comes after the US said it would be sending 2,000 more troops to Poland and Germany in the coming days.

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