Ukrainian Prime Minister Arseny Yatsenyuk has told ITV News Europe Correspondent Emma Murphy that Russia's actions are no longer a threat but "a declaration of war".
He said: "This is not a threat, this is actually a declaration of war to my country and we urge President Putin to pull back his military."
Pro-Russia activists recaptured administrative headquarters in the Ukrainian city of Donetsk and flew the Russian flag from its roof.
ITV News' Europe Correspondent describes the tense atmosphere surrounds a central government building in Donetsk .
New footage obtained by ITV News shows Russian troops firing warning shots as Ukrainian soldiers approached during a tense stand-off today.