Ukraine's second-largest city, Kharkiv, and large parts of the eastern Donetsk region were suffering from widespread blackouts on Sunday as Ukrainian forces continued their counteroffensive. 

Ukrainian President Volodymyr Zelenskyy blamed Russian attacks on "critical infrastructure," saying that their goal is to "deprive people of light & heat." The Zaporizhzhia, Dnipropetrovsk, and Sumy regions were also suffering from partial blackouts. 

Russian forces retreated from dozens of settlements in the northeast Kharkiv region over the weekend, losing important supply lines. 

Kharkiv Mayor Ihor Terekhov accused Russian forces of "cynical revenge" for allegedly attacking civilian infrastructure as they left. 

The Ukrainian counteroffensive, which originally launched in late August and initially focused on the southern Kherson region, has shifted to the northeast in recent days. 

UKRAINE AID IS WORKING AND RUSSIA'S INVASION IS LOSING GROUND

Ukrainian Defense Minister Oleksii Reznikov appeared confident that Russia's morale would collapse "like an avalanche" with "each line of defense falling one after the other." 

"I am convinced that after a few more successes at the front, even small victories, the Russian troops will start fleeing," Reznikov said Saturday in an interview translated by Pravda. "Today we have been destroying their supply chains, warehouses, and so on." 

General Valeriy Zaluzhnyi, Ukraine's military chief, claimed that forces have retaken more than 1,150 square miles since the start of the counteroffensive. 

Reuters contributed to this report.