"We do have information that the Russians are likely to want to fabricate a pretext for an invasion," said Pentagon spokesperson John Kirby.

He told reporters that Washington believed the Russian government plans to stage an attack by the Ukraine military or intelligence forces "against Russian sovereign territory, or against Russian speaking people."

The latter could refer to the sizeable Russian-speaking population inside Ukraine.

"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," he said.

That could allow Moscow, which has amassed more than 100,000 troops and heavy offensive arms on Ukraine's border, with an excuse for invading.

Part of the plan would be to make the Ukrainian military equipment used in it appear to be supplied by the West, he said, further justifying Russian reprisals against Ukraine.

"We've seen these kinds of activity by the Russians in the past and we believe it's important when we see it like this that we can call it out," Kirby said.

"I would just say that our experience is that very little of this nature is not approved at the highest levels of the Russian government," Kirby said about the purported plan.