The Kiev Post confirmed two people died as a result of gunshot wounds and a third person died from injuries sustained in a fall during ongoing protests in the Ukrainian capital.
"We are shocked to hear the latest news from Ukraine about deaths of protesters, and express our deepest condolences to their families," Barroso said in a statement. "We deplore in strongest possible terms the use of force and violence, and call on all sides to immediately refrain from it, and start taking steps that would help de-escalate the situation."
A Ukrainian decision in November to suspend efforts to sign free trade and association agreements with the European Union sparked massive protest in Kiev. Demonstrations turned violent this week after the government endorsed legislation meant to restrict protests.
U.N. High Commissioner for Human Rights Navi Pillay said Tuesday events unfolding in Ukraine were "very worrying."
Ukraine is a former Soviet republic. President Viktor Yanukovych said the November decision was made to protect economic ties to Russia.
"We are genuinely concerned about where these developments are taking Ukraine and will continue following closely these developments, as well as assessing possible actions by the EU and consequences for our relations," Barroso said.