Due to the possibility of Russian military action, the State Department has ordered families of US embassy employees in Kyiv, Ukraine, to leave the country, as well as authorized some US government employees to leave.

A State Department official told reporters on Sunday night that Russian military action anywhere in Ukraine would have a significant impact on the embassy’s ability to provide consular services, including assistance to US citizens leaving Ukraine. The State Department is urging those who are able to leave to do so on commercial flights.

Due to Russia’s ongoing military buildup and disinformation campaigns, the decisions were made with extreme caution, according to a separate senior State Department official.

According to the official, the State Department does not have a “solid number” of Americans in Ukraine because no one is required to register with the embassy while there.

Russia has amassed over 100,000 troops on Ukraine’s border, and while the US does not know if Russian President Vladimir Putin has decided to invade or if an invasion is imminent, he has built the military capacity to invade at any time, according to one of the officials.

According to the Russian Ministry of Defense, the concern has grown as Russian forces have entered Belarus, just north of Ukraine, to conduct joint military exercises.

“If Russia chooses to engage in additional military aggression, it has the option of launching the attack from various directions based on where it can launch these incursions against Ukraine,” one official said.

Because of COVID-19, the State Department’s travel advisory to Ukraine was already at level four, the highest level, but the advisory was updated to urge citizens not to travel to the country due to concerns about the possibility of significant Russian military action against Ukraine.

According to the official, if an incursion occurs, security conditions along occupied Crimea and eastern Ukraine are unpredictable and could deteriorate at any time. Though Crimea and the eastern parts of Ukraine are of particular concern, Russian military action anywhere in Ukraine would severely impact the embassy’s ability to provide services.

The United States authorized an additional $200 million in defensive aid last month, and the first shipment of lethal aid for Ukraine’s defensive forces arrived in Kyiv on Saturday.

On “Face the Nation” on Sunday, US Secretary of State Antony Blinken said that if Russia’s military forces invade Ukraine, there will be “massive consequences.”

President Biden said last week that it was his “guess” that Russia would invade Ukraine, and the White House attempted to backtrack on comments he made at a press conference on Wednesday that suggested there might be divisions among Western nations about the consequences Russia might face if it launched a “minor incursion” into Ukrainian territory.

Russia’s government has consistently denied any plans to attack Ukraine, but it has also left open the possibility of unspecified “military action” if the US and the West refuse to grant what Putin has referred to as “security guarantees” constraining NATO’s actions in the region.

On Monday, Russian Foreign Ministry spokeswoman Maria Zakharova said that staffing at the US Embassy in Kyiv was “a question for the American side,” but that it had more to do with “how they are building their information agenda” than actual security concerns.

Britain, which has closely mirrored US rhetoric on Ukraine, said Monday that it, too, was withdrawing some of its embassy staff and their dependents from Kyiv due to “a growing threat from Russia,” but that the British Embassy would remain open “and will continue to carry out essential work.”

Other European nations, however, have been hesitant to support the level of sanctions proposed by the US in response to any Russian military action against Ukraine, and on Monday, top European Union diplomat Josep Borrell said the bloc was “not going to do the same thing” as the US and the UK with its embassy staff, “because we don’t know any specific reasons.” Even Ukraine appeared uncomfortable with the latest U.S. move.