The US has ordered the relatives of its embassy staff in Ukraine to leave amid rising tension in the region.
The State Department has also given permission for non-essential staff to leave and urged US citizens in Ukraine to consider departing.
In a statement, it said there were reports that Russia is planning significant military action against Ukraine.
Russia has denied claims that it is planning to invade Ukraine.
The country has moved 100,000 troops near its border with Ukraine.
It has seized Ukrainian territory before, when it annexed Crimea in 2014, after the country overthrew their pro-Moscow president.