WASHINGTON - The State Department ordered the departure of all family members of U.S. Embassy personnel serving in Kyiv on Sunday, citing the "threat of Russian military action." 

The department also told nonessential staff they can leave the country - a decision that underscores the growing fears in Washington of an imminent military invasion of Ukraine by Moscow as it amasses tens of thousands of Russian troops around Ukraine's borders.

The volatile atmosphere is the latest indication that efforts to de-escalate the crisis have faltered following talks between Secretary of State Antony Blinken and Russian Foreign Minister Sergey Lavrov in Geneva on Friday.

"The security conditions, particularly along Ukraine's borders, in Russia-occupied Crimea, and in Russia-controlled eastern Ukraine, are unpredictable and can deteriorate with little notice," the department said in a statement. "U.S. citizens in Ukraine should consider departing now using commercial or other privately available transportation options."

The departure of family members and some nonessential staff comes as the Biden administration weighs sending thousands of U.S. forces, as well as armaments, to reinforce NATO allies in Poland and the Baltics, according to a U.S. official, who cautioned that a decision on such a deployment has not been made. The administration is not considering sending U.S. forces to Ukraine.

The Biden administration has regularly said that if Russia invades Ukraine, the United States will be forced to put more forces and weapons in allied nations along Russia's periphery - the opposite of what Russian President Vladimir Putin says he wants.

But Russia has moved forces, armored personnel carriers and fighter jets to Belarus, allegedly to carry out joint military exercises in coming weeks. Military analysts worry the exercises could be a ruse to launch an attack on Ukraine across its northern border from Belarusian territory. The border with Belarus is just a few hours north of Kyiv.

The deployments in Belarus have also alarmed the NATO countries on the alliance's eastern flank, three of which - Poland, Latvia and Lithuania - share a border with Belarus and face a threat from the Russian buildup there.

The Baltic nations - Estonia, Lithuania and Latvia - have been pushing for a larger U.S. troop presence on their territory to deter Russia from invading. In a letter to U.S. lawmakers, reported by Politico, top Lithuanian officials wrote that effective deterrence against Russia can be achieved only by having forces already in place in the nation. The United States already has about 200 military trainers in Ukraine, which Moscow has characterized as a threat to its security.

U.S. officials declined to offer more details about why the departure order was being made now, other than relaying President Joe Biden's recent remark that a Russian invasion "could happen at any time."

U.S. officials say they have intelligence of a Russian plan to invade Ukraine but acknowledge they don't know Moscow's ultimate intentions.

On Saturday, Britain accused the Russian government of having plans to install a pro-Russian Ukrainian politician in Kyiv in the event that Ukraine's pro-Western government collapses. The Russian Foreign Ministry has denied any intention to attack Ukraine and has accused Western governments of increasing tensions in the region through disinformation.

U.S. officials stressed that the U.S. Embassy in Kyiv will remain open and that Washington continues to support Ukraine in the face of Russian "aggression." They refused to provide the number of U.S. citizens who are in Ukraine.

The State Department modified its travel advisory on Sunday to carry a more urgent warning due to the coronavirus and "increased threats of Russian military action."

The actions fall short of an evacuation order of U.S. personnel.

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The Washington Post's Dan Lamothe contributed to this report.