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
Police in Ukraine have been resting following violent clashes with anti-government protesters in Independence Square in Kiev.
Twenty-five people were killed during the violence as European leaders expressed concern over the deteriorating situation.
Ukrainian president Viktor Yanukovych blamed opposition leaders for the latest unrest.
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.