Governor Oleh Syniehubov said the incident took place near the town of Derhachi, about 40 km (25 miles) from Hlyboke one of the border settlements where Russia opened a new front in the war in May.
Ukraine’s military halted the Russian offensive there, rushing in reinforcements after Russia pushed up to 10 km (six miles) into the border areas.
Thousands of people have been killed since Russia launched its full-scale invasion of Ukraine February 2022.