The State Department says it is closing its embassy in the Ukrainian capital of Kyiv and relocating all remaining staff members to the city of Lyiv as fears mount of a potential Russian invasion.
Lyiv is located on Ukraine and Poland's border. It's about 300 miles west of Kyiv.
The move comes as Russia has amassed more than 100,000 troops on the eastern border of Ukraine. On Friday, White House officials said they believe that Russia has amassed enough troops on the Ukrainian border to conduct large-scale military operations at "any time."
Previously, analysts believed that Russia would wait to conduct any military action until after the Winter Olympic Games end this week as a gesture of goodwill to host China. But officials now say that it's possible an invasion could occur in the days ahead.
The Pentagon on Friday ordered an additional 3,000 U.S. troops to Poland to reassure allies.
On Saturday, President Joe Biden spoke for an hour with Russian President Vladimir Putin. During the call, the White House says Biden warned that an invasion of Ukraine would "produce widespread human suffering and diminish Russia's standing."
Biden also warned that the U.S. and its allies would respond to an invasion with "swift and severe" military actions and sanctions.