More than 100,00 Russian troops are now surrounding Ukraine’s borders. Security officials in the United States have warned this buildup could be a sign that Russia plans to attack Ukraine in the coming days.

“We cannot perfectly predict the day, but we have now been saying for some time that we are in the window, and an invasion could begin, a major military action could begin by Russia in Ukraine any day now — that includes this coming week, before the end of the Olympics,” National Security Advisor Jake Sullivan said during an interview with CNN.

The United States Embassy in Ukraine has urged all Americans to leave the eastern European nation.

“I would hate to see them get caught in a cross-fire if in fact [Russia] did invade,” President Biden said. “And there’s no need for that, and if I had anyone there I’d say, ‘Leave.’”

“Use some common sense,” Senator Bill Cassidy (R-LA) said during a Fox News interview. “We should not be endangering our soldiers or Marines, et cetera, because somebody decides not to evacuate until after the fact. Get out. If there’s a pending invasion, use common sense. Leave.”

BBC reported Ukraine has called for a meeting with Russia and other members of the Organization for Security and Co-operation in Europe (OSCE) so Russia can explain its troop buildup. Under the terms of the Vienna Document, OSCE members can ask for information on each others military activities. Russia has ignored written requests for the information, leading Ukraine to formally ask for a meeting.