Three Ukrainian servicemen have been killed and 12 wounded in fresh clashes between government forces and Russian-backed separatists despite a ceasefire, a spokesman for Kiev's military said on Friday.

"In the past 24 hours we have lost three Ukrainian heroes, another 12 have been wounded, as a result of intense military activity," said military spokesman Andriy Lysenko, adding that casualties had been heaviest in fighting near the rebel-controlled city of Donetsk.