Ukraine's armed forces claim to have killed "around 100" rebel fighters near the eastern town of Snizhne.
Defence officials said government forces had also destroyed 11 missile systems and tanks but the claims could not be immediately verified.
While rebels said they had seized two settlements west of Snizhne and captured 13 Ukrainian troops, including three officers.
More top news
Did the International Space Station take a wrong turn?
The wife of a British aid worker held by Islamic State militants has recorded a message to his captors appealing for his life to be spared.
Even if you're having a tough day in the office, it's unlikely to be as difficult as the one facing the director of the US Secret Service.