Pro-Russian rebels firing mortar shells and grenades killed 14 Ukrainian soldiers today, the blackest day yet for the military and a dramatic ratcheting up of tensions just three days before a crunch election.
The attacks in the eastern industrial belt near the Russian border underscored the difficulties of the embattled Kiev government in resolving a crisis that is threatening to tear the country apart.
Ukraine's Prime Minister Arseniy Yatsenyuk accused Russia of trying to "escalate the conflict" and disrupt Sunday's vote, calling on the UN Security Council to hold an urgent meeting on the crisis.
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Adding to the chaos in the east, armed separatists seized four coal mines in the first such confirmed attack on the main economic engines of the former Soviet republic.
Western governments have pressured Russia not to meddle in the snap election, seen as crucial to preventing all-out civil war erupting on Europe's eastern flank.
Russia set Western nerves on edge when it massed some 40,000 troops on the border, raising fears of an invasion into eastern Ukraine after its seizure of the Black Sea peninsula of Crimea in March.
Russia's defence ministry today said four trains and more than a dozen planes were taking troops and equipment away from the border in what President Vladimir Putin said were measures to create "favourable conditions" for Sunday's election.
NATO chief Anders Fogh Rasmussen said he had seen some evidence of limited Russian troop activity that he hoped was "the start of a full and genuine withdrawal".
But rebels in Ukraine's heavily-Russified eastern industrial regions of Donetsk and Lugansk are showing no signs of scaling back resistance to what they and the Kremlin regard as an illegitimate government in Kiev.
The Ukrainian defence ministry said the worst of the two overnight attacks saw the insurgents blow up a military vehicle after volleying mortar shells and grenades at a roadblock set up by government troops near the town of Volnovakha in the Donetsk region.