Russia’s claim that it is moving troops away from the border with Ukraine is “false”, according to a senior US official, who added that 7,000 extra troops have arrived in recent days.
The official also said that Russia could launch a “false” pretext to invade Ukraine “at any moment”.
Moscow says it is moving troops away from the Ukrainian border after the completion of military exercises.
But Western officials say they have seen no evidence to support the claim.
Russia denies planning to invade Ukraine, despite having amassed well over 100,000 troops near the border.
“Yesterday, the Russian government said it was withdrawing troops from the border with Ukraine,” a senior White House official told journalists on Wednesday. “They received a lot of attention for that claim, both here and around the world. But we now know it was false.”
The official – quoted by several news agencies – said that as many as 7,000 more Russian troops have been moved to Ukraine’s borders in recent days, with some arriving as recently as Wednesday.
Russia calls Western concern over an invasion “hysteria”. On Wednesday, its defence ministry published a video purporting to show tanks leaving Crimea, which Russia annexed from Ukraine in 2014.
But Ukraine and Western countries have cast doubt on the claims that Russian troops are moving away from the border, with Ukrainian President Volodymyr Zelensky telling the BBC: “We don’t see any troop withdrawal yet, we just heard about it.”
Nato Secretary-General Jens Stoltenberg has also said there are no signs that Russian forces are de-escalating, saying on Wednesday that the threat from Russia had become a “new normal”.
Speaking at a summit of Nato defence ministers in Brussels, Mr Stoltenberg said the alliance was considering setting up new battle groups – the smallest type of self-sufficient military units – in central and south-eastern Europe.
He said this was part of ongoing measures to bolster European defence – on which $270bn (£199bn) had been spent since 2014 – although he attempted to reassure Russia that Nato was not a threat.
France had offered to lead one such battle group in Romania, he said.
Russia’s foreign ministry said it was “no longer interested” in Mr Stoltenberg’s statements.
Crisis could cast a longer shadow
This was a bleak forecast for the future from Nato’s secretary-general.
Jens Stoltenberg described it as the most serious security crisis in Europe since the end of the Cold War. And he made clear that the threat hadn’t gone away.
Even if President Putin doesn’t give the order to attack, there are still signs this crisis will cast a much longer shadow.
Mr Stoltenberg said Russia’s military build-up showed Moscow was prepared to contest European security with the use of force.
That “new normal” could also mean Nato increasing its military posture. Mr Stoltenberg has tasked Nato military planners to look at setting up new battle groups on the alliance’s eastern flank – in Romania and the Black Sea region.
However, no final decision has yet been taken and Nato insists reinforcements would only be sent to act as a deterrent.
Nato is still calling on Russia to engage in dialogue to reduce tensions. But if diplomacy doesn’t work the danger is both sides will end up with their armies doing the talking.
The scepticism over Russia’s claimed withdrawal was also echoed in the UK. UK Prime Minister Boris Johnson told the UN Secretary-General in a phone call there was “currently little evidence of Russia disengaging”, while his defence intelligence chief Lt-Gen Jim Hockenhull said that, on the contrary, Russia was continuing to build up its forces.
“This includes sightings of additional armoured vehicles, helicopters and a field hospital moving towards Ukraine’s borders,” he said. “Russia has the military mass in place to conduct an invasion of Ukraine.”
Russia and Ukraine have deep cultural and historic ties, and both were part of the former Soviet Union.
Russian President Vladimir Putin wants assurances that Ukraine will not join Nato because he sees any expansion of it as a threat. Nato has rejected that demand.
Mr Putin said on Tuesday that Russia did not want war, but demanded that the issue of Nato membership be addressed now, even though Ukraine is a long way from even starting an application to join the alliance.
Mr Stoltenberg said Nato remained prepared for dialogue, and it was not too late for Russia to “step back from the brink of conflict”.
Separately, Ukraine has been marking a so-called day of unity, with national blue and yellow flags raised throughout the country.
President Volodymyr Zelensky declared the day after US intelligence reports that Russia could attack Ukraine on Wednesday.
On Tuesday the websites of Ukraine’s defence ministry, armed forces and two banks came under a cyber-attack. The cause is not clear but Ukraine has suffered large-scale attacks before on its online infrastructure and has pointed the finger at Russia.
Russia’s government, however, has denied any involvement.
There has long been concern that, rather than a full-scale invasion, Russia could use less obvious means to destabilise Ukraine, for example through cyber-attacks on critical infrastructure.
And on Wednesday the US state department warned that Russian officials were planting stories in the media aimed at influencing public opinion in the event of an invasion.
Spokesman Ned Price expressed concern at Mr Putin’s claim that “genocide” was taking place in eastern Ukraine.
Meanwhile Russian officials said they were investigating alleged mass graves containing hundreds of civilians in the conflict zone.