By ELENA BECATOROS, OLEKSANDR STASHEVSKYI and RICARDO MAZALAN Associated Press

KYIV, Ukraine (AP) — Workers digging through the rubble of an apartment building in Mariupol found 200 bodies in the basement, Ukrainian authorities said Tuesday, as more horrors come to light in the ruined city that has seen some of the worst suffering of the 3-month-old war.

The bodies were decomposing and the stench hung over the neighborhood, said Petro Andryushchenko, an adviser to the mayor. He did not when they were discovered, but the sheer number of victims makes it one of the deadliest known attacks of the war.

Heavy fighting, meanwhile, continued in the Donbas, the eastern industrial region that Moscow’s forces are intent on seizing. Russian troops intensified their efforts to encircle and capture Sievierodonetsk and neighboring cities.

Mariupol was relentlessly pounded during a nearly three-month siege that ended last week after some 2,500 Ukrainian fighters abandoned a steel plant where they had made their stand. Russian forces already held the rest of the city, where an estimated 100,000 people remain out a prewar population of 450,000, many of them trapped during the siege with little food, water, heat or electricity.

At least 21,000 people were killed in the siege, according to Ukrainian authorities, who have accused Russia of trying to cover up the horrors by bringing in mobile cremation equipment and by burying the dead in mass graves.

During the assault on Mariupol, Russian airstrikes hit a maternity hospital and a theater where civilians were taking shelter. An Associated Press investigation found that close to 600 people died in the theater attack, double the figure estimated by Ukrainian authorities.

Ukrainian President Volodymyr Zelenskyy accused the Russians of waging “total war” and seeking to inflict as much death and destruction as possible on his country.

“Indeed, there has not been such a war on the European continent for 77 years,” Zelensky said, referring to end of World War II.

Moscow-backed separatists have fought Ukrainian forces in the Donbas for eight years and hold large swaths of territory. Sievierodonetsk and neighboring cities are the only part of the Donbas’ Luhansk region still under Ukrainian government control.

Russian forces have achieved “some localized successes” despite strong Ukrainian resistance along dug-in positions, British military authorities said.

Moscow’s troops also took over the town of Svitlodarsk and raised the Russian flag there, Ukrainian media reported. Svitlodarsk is about 50 kilometers (31 miles) southeast of the strategically important city of Kramatorsk.

Two top Russian officials appeared to acknowledge that Moscow’s advance has been slower than expected, though they vowed the offensive would achieve its goals.

Nikolai Patrushev, secretary of Russia’s Security Council. said the Russian government “is not chasing deadlines.” And Defense Minister Sergei Shoigu told a meeting of a Russia-led security alliance of former Soviet states that Moscow is deliberately slowing down its offensive to allow residents of encircled cities to evacuate — though forces have repeatedly hit civilian targets.

As Kharkiv, Ukraine’s second-largest city, recovers from weeks of weeks of relentless bombardment, residents formed long lines to receive rations of flour, pasta, sugar and others staples this week. Moscow’s forces withdrew from around Kharkiv earlier this month, pulling back toward the Russian border.

Galina Kolembed, the aid distribution center coordinator, said that more and more people are returning to the city. Kolembed said the center is providing food to over 1,000 people every day, a number that keeps growing.

“Many of them have small kids, and they spend their money on the kids, so they need some support with food,” she said.

Becatoros reported from Kramatorsk, Ukraine. Associated Press journalists Yuras Karmanau in Lviv, Andrea Rosa in Kharkiv, Danica Kirka in London and other AP staffers around the world contributed.