Ukraine's acting president has warned Russia that troop movements outside its naval base in Crimea would be seen as an "act of aggression". Armed men seized regional government headquarters and parliament and the Russian flag is flying from buildings
European Union foreign ministers have agreed to move ahead with sanctions including visa bans and asset freezes on those responsible for the violent clashes in Ukraine.
After leaving an emergency gathering in Brussels, Italian Foreign Minister Emma Bonino said the decision had been agreed with her French, German and Polish counterparts, who are in Kiev negotiating with Ukrainian President Viktor Yanukovich.
She said: "The decision is to proceed very rapidly, in the next hours, to a visa ban and asset freeze on those who have committed the violence."
Ukraine's interim President has expressed concerns about signs of separatism as opposition in Russian-speaking regions grows.
Hundreds of Ukrainians and journalists flocked to the presidential palace, as reports emerged that President Yanukovich had left the city.
Vitali Klitschko was met with boos from anti-government protesters, as he attempted to convince them a peace deal is best course of action.