At least 50 pro-Russian separatists were killed during clashes with army forces in the towns of Vodyanoe and Opitnoe in eastern Ukraine, the Ukrainian defense ministry said in a statement Friday.
The statement also said the army detained five people and destroyed four pro-Russian separatist vehicles.
Tensions increased when Ukraine's military confirmed it had abandoned Donetsk Airport to separatist militias on Wednesday.
On Thursday, at least eight people were killed and 13 others were wounded after two mortar rounds landed near a crowded bus station in Donetsk, according to the Organization of Security and Cooperation in Europe.
More than 5,000 people have lost their lives in the conflict which began in April 2014, according to the UN.