The EU says it is putting on hold work on a key trade agreement with Ukraine, saying the government's arguments have "no grounds in reality". Protesters have taken to the streets in support of the agreement, which was rejected by the government.
There have been dramatic scenes near the presidential palace in Kiev with protesters throwing flares at riot police, who responded with stun grenades.
Riot police have been pushing protesters out of square in front of the building and reportedly beating those who refused to leave.
The clashes follow an apparently peaceful rally in the city's Independence Square earlier today.
There is an urgent need for de-escalation in Ukraine as President Yanukovich tries to calm a country bitterly divided over years of history.
Ukraine's political and economic landscape is stuck between old Soviet masters in Russia and the democratising ideals offered by the EU.