The State Department updated its travel advisory for Ukraine Monday to “do not travel,” warning Americans not to make trips there due to “increased threats from Russia” as it continues to build up its forces along Ukraine’s borders. “U.S. citizens should be aware of reports that Russia is planning for significant military action against Ukraine,” the State Department alert states, adding that security conditions “can deteriorate with little notice” and could impact the U.S. Embassy’s ability to help Americans flee Ukraine should a further military crisis unfold. The State Department had previously issued an advisory in October that warned Americans against traveling there due to COVID-19 infection risk.

The warning comes as Russia has been amassing troops along Ukraine’s borders, in what U.S. officials say could be President Vladimir Putin’s preparations for invasion into Ukraine, seven years after it annexed Crimea and Russian-backed military intervention in the Donbass. President Joe Biden’s efforts to ease tensions with Russia—by threatening economic sanctions and pulling back on the Nord Stream 2 pipeline—have so far not convinced Russia to back down. Without U.S. and western military aid, Ukraine likely won’t withstand invasion, U.S. lawmakers tell The Daily Beast, and in the meantime they are pressuring the White House and the Department of Defense to boost lethal aid to Ukraine to try to stop the crisis in its tracks.