"In total it is known that 14 people died but the bodies of four of them have not been identified and could be Ukrainian soldiers or terrorists," military spokesman Oleksiy Dmytrashkivsky told media.
He added that "so far we are talking about 10 Ukrainian servicemen dead" in the clash, in the town of Shakhtarsk some 25 kilometres (15 miles) from the MH17 site.
Earlier the Ukrainian military had said its troops were ambushed by insurgent fighters.
The deadly fighting shattered a brief lull across the war-torn region as international experts headed to the wreckage of the downed plane to try to begin a stalled investigation into the attack on the passenger jet.
The Ukrainian military said it was relaunching a broader offensive against separatist fighters following a day-long ceasefire but insisted troops would not carry out operations in the immediate vicinity of the crash site.
The military said Friday that it had made fresh gains by taking the village of Novyi Svit, some 25 kilometres southeast of the rebel stronghold of Donetsk, and was waging operations to secure the volatile border with Russia.