Ukraine say at least ten of its soldiers have been killed by pro-Russian separatists near the eastern town of Shakhtarsk, in the region where a Malaysian airliner was brought down last month.
Military officials say a paratrooper unit came under mortar and tank fire overnight.
Earlier Ukrainian television reported that 20 servicemen had been killed in the attack, saying a Grad missile had been fired.
It comes as Belarus pursues diplomatic efforts to resolve the crisis.
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