The United States has accused Russia of positioning saboteurs to carry out a "false-flag" operation in eastern Ukraine.
The White House said the move would involve sabotaging Russia's own forces, creating a pretext to invade.
It said the Russian operatives have been trained in urban warfare and explosives.
US intelligence estimated a Russian military invasion could begin between mid-January and mid-February.
Jen Psaki, the White House press secretary, said: "We are concerned that the Russian government is preparing for an invasion in Ukraine that may result in widespread human rights violations and war crimes should diplomacy fail to meet their objectives.
"We have information that indicates Russia has already prepositioned a group of operatives to conduct a false-flag operation in eastern Ukraine.
"The operatives are trained in urban warfare, and in using explosives to carry out acts of sabotage against Russia's own proxy forces."
US intelligence suggested Russia has also been laying groundwork through a social media disinformation campaign, which frames Ukraine as an aggressor.
That campaign paints Ukraine as preparing an imminent attack against Russian-backed forces in eastern Ukraine.
The intelligence has been shared with allies.
A Pentagon spokesman said the intelligence was "very credible."
A US official said: "As part of its plans Russia is laying the groundwork to have the option of fabricating a pretext for invasion, including through sabotage activities and information operations, by accusing Ukraine of preparing an imminent attack against Russian forces in eastern Ukraine."
Another official told CNN: "The Russian military plans to begin these activities several weeks before a military invasion, which could begin between mid-January and mid-February. We saw this playbook in 2014 with Crimea."
It followed comments on Thursday by Jake Sullivan, Joe Biden's national security adviser.
Mr Sullivan said: "Our intelligence community has developed information, which has now been downgraded, that Russia is laying the groundwork to have the option of fabricating the pretext for an invasion.
"We saw this playbook in 2014. They are preparing this playbook again and we will have further details on what we see as this potential laying of the pretext to share over the course of the next 24 hours."
Speaking in Washington an aide to Ukraine's president Volodymyr Zelensky said he has proposed three-way talks with Joe Biden and Vladimir Putin amid fears of invasion.
Andriy Yermak said: "President Zelensky proposed to President Biden and we think it can be worked to organise a trilateral meeting, maybe by videoconference, between President Biden, President Zelensky and President Putin.
"We are still waiting for the reaction on this, I think, from the Russian side. But our American partners take our proposal with some interest."
Mr Biden and Putin have spoken twice by telephone amid the tensions.
Mr Biden has warned of devastating economic sanctions if Russia invades.