KYIV, Ukraine — Russian forces are stepping up their strikes in a fiercely contested region of eastern Ukraine, worsening the already tough conditions for residents and the defending army following Moscow’s illegal annexation and declaration of martial law in Donetsk province, Ukrainian authorities said.

The attacks have almost completely destroyed the power plants that serve the city of Bakhmut and the nearby town of Soledar, Pavlo Kyrylenko, the region’s Ukrainian governor, said. Shelling killed one civilians and wounded three, he reported late Saturday.

“The destruction is daily, if not hourly,” Kyrylenko said in a state television interview.

Moscow-backed separatists controlled part of Donetsk for nearly eight years before Russia invaded Ukraine in late February. Protecting the separatists’ self-proclaimed republic there was one of Russian President Vladimir Putin’s justifications for the invasion, and his troops have spent months trying to capture the entire province.

While Russia’s “greatest brutality” was focused in the Donetsk region, “constant fighting” continued elsewhere along the front line that stretches more than 1,000 kilometers (620 miles), Ukrainian President Volodymyr Zelenskyy said in his nightly video address.

Between Saturday and Sunday, Russia’s launched four missiles and 19 airstrikes impacting more than 35 villages in seven regions, from Chernihiv and Kharkiv in the northeast to Kherson and Mykolaiv in the south, according to the president’s office.

Russia has focused on striking energy infrastructure over the last month, causing power shortages and rolling outages across the country. The capital, Kyiv, was scheduled to have hourly blackouts rotating Sunday in various parts of the city of some 3 million and the surrounding region,

Rolling blackouts also were planned in the Chernihiv, Cherkasy, Zhytomyr, Sumy, Kharkiv and Poltava regions, Ukraine’s state-owned energy operator, Ukrenergo, said in a Telegram post.

More positive news was the re-connection of the Zaporizhzhia Nuclear Power Plant to Ukraine’s power grid, local media reported Sunday. Europe’s largest nuclear plant needs electricity to maintain vital cooling system, but it had been running on emergency diesel generators since Russian shelling severed its outside connections,

In the Donetsk city of Bakhmut, some 15,000 remaining residents were living under daily shelling and without water or power, according to local media. The city has been under attack for months, but the bombardment picked up after Russian forces experienced setbacks during Ukrainian counteroffensives in the Kharkiv and Kherson regions.

In Kharkiv, officials are working to identify bodies found in mass graves after the Russians withdrew, Dmytro Chubenko, a spokesperson for the regional prosecutor’s office, said in an interview with local media.

DNA samples have been collected from 450 bodies discovered in a mass grave in the city of Izium, but the samples need to be matched with relatives and so far only 80 people have participated, he said.