Live updates: follow the latest news on Russia-Ukraine
White House National Security Adviser Jake Sullivan said the US anticipated that Russian commanders were now moving troops from northern Ukraine to the region around the Donbas region in eastern Ukraine.
Mr Sullivan said that Moscow was also refocusing operations on parts of southern Ukraine.
"Russian forces are already well on their way of retreating from Kyiv to Belarus, as Russia likely prepares to deploy dozens of additional battalion tactical groups constituting tens of thousands of soldiers to the frontline in Ukraine's east," he said.
Despite the troop movement after Russia's "retreat" from Kyiv, Moscow will continue to launch air strikes against the capital, and in Odesa, Kharkiv and other cities across Ukraine, to "frankly, cause terror", Mr Sullivan said.
"We should be under no illusions that Russia will adjust its tactics, which have included and will likely continue to include wanton and brazen attacks on civilian targets," he said.
Mr Sullivan said the US would impose more sanctions against Russia this week.
On Monday, US President Joe Biden insisted on his claim that Russian President Vladimir Putin is a "war criminal" and called for a war crimes trial after the civilian killings in the Ukrainian town of Bucha.
The US and more than 40 other countries are working together to investigate possible breaches and abuses after the passage of a resolution by the UN refugee agency to establish a commission of inquiry.
The International Criminal Court, an independent body in the Netherlands to which the US is not a signatory, is also conducting an investigation.
Mr Sullivan said he had yet to see evidence that Russian atrocities had risen to the level of genocide. He said consultations might take place at the ICC or another venue.
The US Senate unanimously approved a resolution last month seeking investigations of Mr Putin and elements of his government for war crimes over the invasion of Ukraine.
Meanwhile, US ambassador to the UN Linda Thomas-Greenfield said the US was seeking Russia's suspension from the Human Rights Council.
"We cannot let a member state that is subverting every principle we hold dear to continue to participate," Ms Thomas-Greenfield said in a tweet.
Mr Biden finds it "ludicrous" that Russia is a member of the council, White House press secretary Jen Psaki said.
AP contributed to this report.