The United States on Sunday ordered the departure of family members of staff at its embassy in Ukraine, citing the continuing threat of military action from Russia.
The U.S. State Department also authorized the voluntary departure of U.S. government employees and said Americans should consider departing immediately.
"We have been in consultation with the Ukrainian government about this step and are coordinating with Allied and partner embassies in Kyiv as they determine their posture," the U.S. Embassy said.
Russia has massed troops near the border with Ukraine prompting tensions with Western powers. Moscow has insisted it has no plans to invade.
The U.S. Embassy in Kyiv warned in a statement that "military action by Russia could come at any time and the United States government will not be in a position to evacuate American citizens in such a contingency, so U.S. citizens currently present in Ukraine should plan accordingly."
The State Department also said it was authorizing the "voluntary departure of U.S. direct hire employees."
The New York Times reported late Sunday that President Joe Biden was considering deploying several thousand U.S. troops to NATO allies in Eastern Europe and the Baltics.
The Pentagon declined to comment on the New York Times report but noted that Pentagon spokesman John Kirby on Friday said, "we're going to make sure that we have options ready to reassure our allies, particularly on -- on NATO's Eastern Flank."
"If there's another incursion and if they need that reassurance, if they need the capabilities to be bolstered, we're going to do that and we're going to make sure that we're -- that we're ready to do that," Kirby said.
U.S. and Russian diplomats made no major breakthrough at talks on Friday.
On Sunday, Britain accused the Kremlin of seeking to install a pro-Russian leader in Kyiv.
The State Department late Sunday also reissued its advisory for Russia warning Americans not to travel, citing "ongoing tension along the border with Ukraine." It also added "given the on-going volatility of the situation, U.S. citizens are strongly advised against traveling by land from Russia to Ukraine through this region."
State Department officials declined to say how many Americans are currently believed to be in Ukraine.
The U.S. Embassy in Ukraine said the decision was made "out of an abundance of caution due to continued Russian efforts to destabilize the country and undermine the security of Ukrainian citizens and others visiting or residing in Ukraine."
The U.S. Embassy in Kyiv is continuing to operate and its Chargé d'Affaires Kristina Kvien remains in Ukraine, State Department officials said.
