A day after the State Department announced it is ordering the evacuation of non-essential staff and families of staffers at the United States’ embassy in Ukraine, the Department of Defense announced Monday it has put 8,500 troops on “heightened alert.” The video above shows the embassy on Monday. Those troops could be deployed to Eastern Europe “to respond to a range of contingencies, including support to the NATO response force, if it is activated.”

“As of now, the decision has been made to put these units on higher alert and higher alert only,” Pentagon spokesperson John Kirby said at a Monday briefing. “No decisions have been made to deploy any forces from the United States at this time.”

In addition to partially evacuating the embassy, the State Department recommended that all U.S. citizens living in Ukraine leave the country and elevated its travel advisory for Ukraine: “Do Not Travel due to the increased threat of Russian military action.”

“These decisions were 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,” a senior State Department official said Sunday. “We have no higher priority than the safety and security of U.S. citizens, and this includes our U.S. Government personnel and their dependents, and the security of our facilities overseas.”

State Department officials stressed the Ukraine embassy will remain open, saying the announcement does not constitute a full evacuation. While the weekend order had been considered for a while, the State Department cited recent reports that Russia was planning significant military action against Ukraine as a reason for the partial evacuation of the embassy.

“Why did we make this decision now? Do we believe a Russian invasion is imminent? As President Biden has said, military action by Russia could come at any time,” the official said. “If Russia chooses further escalation, then 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.”

NATO is also preparing for potential military action. On Monday, the alliance announced multiple actions it is taking “to enhance deterrence and defense in eastern Europe,” including:

• Denmark sending a frigate to the Baltic Sea and deploying four F-16 fighter jets to Lithuania
• Spain sending ships to join NATO naval forces
• The Netherlands sending two F-35 fighter aircraft to Bulgaria

According to NATO, Spain “is considering sending fighter jets to Bulgaria,” “France has expressed its readiness to send troops to Romania,” and the U.S. has “made clear that it is considering increasing its military presence in the eastern part of” NATO territory.

“I welcome Allies contributing additional forces to NATO,” Secretary General Jens Stoltenberg said in a Monday statement. “NATO will continue to take all necessary measures to protect and defend all Allies, including by reinforcing the eastern part of the Alliance.”