During Wednesday's confrontations, riot police violently beat and shot at protesters, volunteer medics and journalists. The Interior Ministry announced that 70 protesters had been arrested.
Prime Minister Mykola Azarov said the police did not have live ammunition and that opposition leaders should be held responsible for the deaths.
City health officials and police said that two people died of gunshot wounds during the clashes Wednesday morning, while the opposition contended as many as five people died. Oleh Musiy, coordinator of the protesters' medical corps, told the Associated Press that four people died of gunshot wounds and the fifth died after falling from a colonnaded gate at a sports arena near the site of the clashes. Health officials contend that man survived and is in the hospital. Hundreds of others were injured in the clashes, Musiy said.
Meanwhile, another protester, Yuri Verbitsky, was found dead in a forest outside Kiev on Wednesday, according to his niece Oksana Verbitska. His friends and supporters believe he was kidnapped.
The United States responded by revoking the visas of Ukrainian officials linked to violence and threatened more sanctions. But it also condemned the extreme-right radical protesters for their aggressive actions. The EU condemned the violence and said it was also considering action against the Ukrainian government.
One of the victims was identified as Sergei Nigoyan, a 20-year-old ethnic Armenian who joined the protests in December after traveling from his home in the eastern city of Dnipropetrovsk. A video shows Nigoyan reciting poetry in the protest camp in Kiev's Independence Square, also known as the Maidan. He then clenched his fist in a victory sign as a yellow-and-blue Ukrainian flag flapped in the background.
A Ukrainian journalist, Kristina Berdinskikh, who has been profiling protesters for several weeks, interviewed Nigoyan in early January.