A Ukrainian military spokesman confirmed that heavily armed separatists attacked a military checkpoint at Volnovakha. Journalists said 11 bodies were observed after the overnight clashes, and a spokesman for acting Ukrainian President Oleksandr Turchynov put the death toll at 13.
Charred Ukrainian military vehicles, including armored personnel carriers, were also seen in the area, and witnesses said about 30 government troops were injured in the attack.
The incidents come four days before a national presidential election in Ukraine, and soon after authorities claimed they have separatists in eastern Ukraine under control. It also came the day after NATO Secretary General Anders Fogh Rasmussen noted Russian troops may be pulling away from their side of the Russian border with Ukraine.
In a statement, the Ukrainian Defense Ministry in Kiev claimed the separatists "ambushed and opened fire on a checkpoint with a mass of small arms, hand grenades and anti-tank mortars," adding an ammunition depot was ignited.
Earlier this week Turchynov said Kiev's military campaign against the rebels in the eastern part of the country was entering its "final phase," which the said would "cleanse the Donestsk and Luhansk regions of terrorists."