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
At least 26 people have now died during violent clashes between police and anti-government protesters in Ukraine.
The Health Ministry said 25 people had been killed in the fighting in the capital, of which nine were police officers, but police later said a 10th officer had died of his wounds.
The interior ministry claimed that five of the dead officers had died of identical wounds from sniper fire to the head and neck.
The country's embattled president has accused the opposition of attempting to "seize power" by means of "arson and murder", while protesters have viewed to remain in Independence Square "until victory".
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.