Three protesters died and seven others were seriously injured during protests Tuesday in Kiev, an opposition member of Ukraine's parliament told CNN.
Speaking from the protesters' medical facility outside the parliament building, Olesya Orobets said ambulances had been barred from the area.
The casualties occurred after protesters set fire to the headquarters of the ruling Party of Regions and as violence roiled the capital for the first time in more than two weeks.
At least seven police officers were hurt, Ukraine's Interior Ministry said.
Thousands of demonstrators have packed Kiev's Independence Square since November, when President Viktor Yanukovych reversed a decision to sign a trade deal with the European Union and instead turned toward Russia.
The unrest intensified after an anti-protest law went into effect. Throngs of demonstrators took to the streets to protest the law.
More than 2,000 people have been injured during the clashes.
A sliver of hope for a restoration of calm had emerged Sunday, when the government agreed to drop charges against demonstrators in exchange for the protesters' agreement to leave Kiev's City Hall and unblock streets in the city center, which they had occupied for almost three months.
But violence re-erupted Tuesday, after the speaker of the parliament would not let opposition members register amendments that would have led to a vote to limit the rights of the President and restore the constitution to the way it was in 2004.