A senior Ukrainian official said Russian forces would enter areas just outside the capital, Kyiv, later on Friday and that Ukrainian troops were defending positions on four fronts despite being outnumbered.

An estimated 100,000 people fled as explosions and gunfire rocked major cities. Dozens have been reported killed.

Russian President Vladimir Putin said he did not plan a military occupation, only to disarm Ukraine.

The United States, Britain, Japan, Canada, Australia and the EU unveiled more sanctions on Moscow on top of penalties earlier this week, including a move by Germany to halt an 11 billion USD gas pipeline from Russia.

EU foreign policy chief Josep Borrell described the bloc's measures as "the harshest package of sanctions they have ever implemented".