Vyatcheslav Ponomarev said the battle broke out at a barricade put up in a village east of Slavyansk, which is under the control of pro-Russian militants.
Separatist gunmen maintain a firm grip over a string of towns across Ukraine's industrial east despite an international deal signed last week demanding they vacate state buildings they are occupying.
Authorities in Kiev say they have suspended military operations against the pro-Moscow rebels until after the Easter holidays in a bid to give the agreement time to stick.