The number of people killed in eastern Ukraine since last April has now topped 6,000, despite successive ceasefires, a UN spokesman said Monday.
German Chancellor Angela Merkel expressed outrage on Thursday over the Ukraine government's crackdown on protesters.
Ukrainian Prime Minister Mykola Azarov said on Wednesday anti-government protests had brought "terrorists" on to the streets and warned that all "criminal actions" would be punished.
Ukraine's prime minister said on Wednesday that anti-government protests had brought "terrorists" onto the streets of Kiev and pledged to punish all "criminal action".
The White House threatened on Sunday to slap sanctions on Ukraine "in response to its use of violence" against protesters.
Ukrainian protesters attacked riot police with sticks, fireworks and smoke bombs in central Kiev on Sunday, triggering another wave of clashes between officers and demonstrators.
Ukraine's state-run energy firm Naftogaz and Russia's gas giant Gazprom have signed an amendment to the gas supply contract, pegging the price of gas at 268.5 US dollars per 1,000 cubic meters.
Protesters demanded Ukraine's interior minister resign on Thursday after an opposition journalist known for documenting the extravagance of the country's political elite was chased down in her car and savagely beaten in a midnight attack.