More than 30 pro-Russian separatists were killed in fighting near the rebel stronghold of Slaviansk in eastern Ukraine, Interior Minister Arsen Avakov said.
"We estimate that the terrorists lost more than 30 people," Avakov wrote on Facebook.
Pro-Russian rebels ambushed Ukrainian forces yesterday, triggering fierce fighting near Slaviansk. Avakov said four Ukrainian servicemen had been killed and 20 wounded.
The pro-Russian rebels said four of their number had been killed in the fighting.