Ukrainian President Volodymyr Zelenskyy said Moscow's massive air and artillery attacks were aimed at destroying the entire Donbas region and urged allies to accelerate the shipment of heavy weapons to match Russia on the battlefield.

The fight for the twin cities of Sievierodonetsk and Lysychansk in Ukraine's Luhansk region is "entering a sort of fearsome climax," said Oleksiy Arestovych, adviser to Zelenskyy. Russia is seeking to capture both Luhansk and Donetsk, which make up the Donbas region — the nation's industrial heartland.

On the diplomatic front, European leaders on Thursday will formally set Ukraine on the long road to EU membership at a summit in Brussels. Though mainly symbolic, the move will help lift morale after four-months of bloody conflict that has killed thousands, displaced millions and destroyed cities.