The United States has intelligence showing that Russia has a plan to fabricate a pretext for invading Ukraine, the Pentagon said Thursday.

Russia has been amassing tens of thousands of troops on its borders with Ukraine but denies that it is planning to invade. Instead, Moscow has accused the United States of escalating tensions by deploying more troops to the region to reinforce NATO's eastern flank.

Pentagon spokesperson John Kirby told reporters there was evidence showing the Kremlin had developed a plot to film a fake attack by Ukraine's military "against Russian sovereign territory, or against Russian speaking people."

"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," to justify an invasion, Kirby said.  

The alleged operation was revealed in declassified intelligence shared with Ukrainian officials and European allies.

"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, and we can, to call it out,'' Kirby said. 

"Our experience is that very little of this nature is not approved at the highest levels of the Russian government," he added. 

'An option' on Moscow's table

US Deputy National Security Adviser Jonathan Finer said it wasn't certain that "this is the route they 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."

"That would involve the deployment of corpses to represent bodies purportedly killed, of people purportedly killed in an incident like this," Finer told broadcaster MSNBC.

British Foreign Minister Liz Truss said the alleged plot was "shocking evidence" of Russian aggression.

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

NATO: 30,000 Russian troops in Belarus

The intelligence was released as Turkish President Recep Tayyip Erdogan offered to mediate between Kyiv and Moscow to ease tensions. 

French President Emmanuel Macron had a phone call with Russian President Vladimir Putin and was scheduled to speak to his Ukrainian counterpart Volodymyr Zelenskyy later in the day.

NATO Secretary-General Jens Stoltenberg, meanwhile, warned that Russia's military buildup on Ukraine's borders was continuing. He said Russian troop numbers in Moscow-ally Belarus were likely to increase to 30,000 — more than at any other point in the last 30 years. 

"Over the last days, we have seen a significant movement of Russian military forces into Belarus. This is the biggest Russian deployment there since the Cold War,'' Stoltenberg told reporters.

He said the deployment there was backed by special forces, advanced fighter jets, Iskander short-range ballistic missiles and S-400 ground-to-air missile defense systems.

Stoltenberg also renewed his call for Russia to "de-escalate,'' and reiterated that "any further Russian aggression would have severe consequences and carry a heavy price.''

NATO has started reinforcing the defenses of its members in the east but says it has no intention of deploying troops to Ukraine, which is not a member of the alliance, in the event of a Russian invasion. 

nm/sms (AFP, Reuters, AP)