Ukraine tensions: Russia invasion could begin any day, US warns

Russia could invade Ukraine "at any time" and American citizens should leave immediately, the US has warned.

An invasion could start with aerial bombing that would make departures difficult and endanger civilians, the White House said on Friday.

Moscow has repeatedly denied any plans to invade Ukraine despite massing more than 100,000 troops near the border.

The US statement prompted countries around the world to issue fresh warnings to nationals in Ukraine.