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 daysç BBC reported.
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 must take real steps toward de-escalation," US President Joe Biden and German Chancellor Olaf Scholz agreed in a phone call on Wednesday, according to the German chancellery.
Russia - which has repeatedly denied planning to invade Ukraine, despite having amassed well over 100,000 troops near the border - calls Western concern over an invasion "hysteria".
Its defence ministry has published images purportedly showing troops and equipment returning to their permanent bases after military exercises.
But according to a senior White House official, thousands more troops have arrived in the area in recent days - including some on Wednesday itself.
Speaking to journalists, the US official cast doubt on Russia's assertions that "it was withdrawing troops from the border with Ukraine".
"They received a lot of attention for that claim, both here and around the world. But we now know it was false."
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