The US has seen indications of Russian troop movements from and into Ukraine's Crimea region on Friday but their numbers are unclear, as are the intentions of those movements, US officials told Reuters, speaking on condition of anonymity.
One US official said some of the movements could be designed to bolster protection of Russian forces there.
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.