Ukrainian police clashed with members of a far-right group who were protesting at a presidential campaign event in Cherkasy on Saturday.
According to a statement from Ukraine's national police, 15 officers were injured in the altercation.
Pictures posted to social media show several injured officers, including police chief Valery Lyuty, who can be seen with a cut to his eye and a bloodstained face.
The protest, staged by the far-right National Corps Party, was planned to coincide with an election campaign event led by Ukrainian President Petro Poroshenko.
When several demonstrators attempted to the rush the stage during Poroshenko's speech, police officers pushed back, sparking the subsequent violence.
An investigation has been launched against the group for "threats of violence" and hooliganism.
Ukraine's presidential election is set for the end of March following a tumultuous political campaign.
Among the three frontrunners for Ukraine's top spot is current president Poroshenko, former prime minister Yulio Tymoshenko, and an actor inexperienced in politics, Volodymyr Zelensky.
Tymoshenko also announced in late February that she had launched impeachment proceedings against Poroshenko following a media expose linking him to a corruption scandal.