Clashes in the economically-vital industrial border regions of Lugansk and Donetsk picked up with renewed vigour when Ukrainian President Petro Poroshenko tore up a 10-day truce because of continuing rebel attacks.
Poroshenko's decision Monday was immediately followed by the launch of a "massive" offensive by Kiev that drew warnings from Russian President Vladimir Putin about his right to protect compatriots in Ukraine.
Donetsk authorities said the eastern city of nearly one million people was shaken overnight by the echoes of blasts from battles raging on its outskirts.
Ukraine's military reported it lost one man in rebel raids that included brief assaults on airfields near Lugansk and the flashpoint city of Kramatorsk.
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A spokesman for Kiev's forces claimed 150 pro-Kremlin gunmen had been "eliminated". Similar unverified claims, which the rebels deny, have been made throughout the conflict.
The uprising in eastern Ukraine was sparked by the ousting in February of a pro-Kremlin administration in Kiev, and was encouraged by Russia's subsequent seizure of Crimea.
So far it has claimed more than 460 lives and left parts of the industrial rustbelt in ruins.
Russia now faces the threat of devastating economic sanctions should Putin fail to explicitly order the militias to lay down their arms.
France and Germany -- still hoping to avoid new punitive steps that would damage their own economies -- are now spearheading efforts to set up new Contact Group discussions that until now have failed to yield results.
US President Barack Obama and British Foreign Secretary William Hague both called on Putin yesterday to make sure the separatists attend the talks.
Unnamed sources told Russian media that the talks had been tentatively scheduled for this evening somewhere in Ukraine.
But Kiev refuses to convene the meeting again in rebel-held Donetsk -- a location backed strongly by Moscow.