Russia Pushes to Take Ukrainian Town Near a Vital Supply Line

KYIV, Ukraine — Moscow is deploying thousands of soldiers to southeastern Ukraine as it renews an assault on a strategically important town that Ukrainian forces have used to harass shipments on a critical Russian supply line that runs from the eastern Donbas region to Crimea.

The town, Vuhledar, has long been in Russia’s cross hairs. It sits at the intersection of the eastern front in the Donetsk region and the southern front in the Zaporizhzhia region, close to the only rail line linking Crimea with the Donbas region. The Ukrainians have used that proximity to lob artillery shells at the trains, limiting Russia’s ability to move men and equipment between the two fronts and, ultimately, to achieve its stated aim of capturing the Donbas, which comprises the provinces of Luhansk and Donetsk.

After a major drive in November failed, with reportedly enormous losses, Russian commanders are once again attacking in and around Vuhledar in hopes of securing the rail line.

“This can be done in only one way — by capturing and occupying Vuhledar, which just ‘hangs’ over this railway line,” said Ivan Yakovina, a Ukrainian journalist. By capturing the “seemingly small and not very significant town,” he said, “Russia would have received a wide logistical artery along the entire front line and, accordingly, the ability to quickly and massively transfer troops from one direction to another.”

In addition to taking control of Donbas, Moscow is intent on keeping control over the so-called land bridge, the slice of occupied territory that connects Russia to Crimea, the peninsula that Moscow has occupied since 2014. Kyiv’s hold on Vuhledar threatens that as well.

Ukrainian officials said that they had repelled the latest assaults, but warned that Russian forces, bolstered by thousands of newly mobilized soldiers, were trying to encircle the town.

“The Russians are not trying to break through the defenses of Vuhledar, but are trying to surround the city from two sides,” the city’s deputy mayor, Maksym Verbovsky, told the Ukrainian news outlet Suspline on Friday. “They managed to advance to some nearby villages, but the Ukrainian military pushed them back to their previous positions.”

The fighting has left yet another Ukrainian city in ruins.

Vuhledar “was destroyed,” Mr. Verbovsky said. “One hundred percent of the buildings were damaged. The entire infrastructure.”

Fewer than 500 civilians and just three children remain, he said, in what had until a year ago been a densely packed industrial town of about 15,000.

Vuhledar takes its name, “gift of coal” in Ukrainian, from the mine on its outskirts. Consisting of a cluster of high-rise apartment complexes on an otherwise empty plain, the town’s elevation, exposure and tall buildings give defenders a distinct advantage.

The ill-fated November campaign was led by the Russian Pacific Fleet’s 155th Guards Naval Infantry Brigade, with reportedly disastrous results. Mediazona, an independent Russian outlet that tracks Russians killed in battle, published an interview with a Russian marine who said that more than 200 soldiers had been killed in just three days. Reports of the defeat gained enough traction that the Kremlin felt compelled to issue a statement denying them.

On Saturday, fighting continued to rage across the eastern front, a situation President Volodymyr Zelensky described as “very difficult” in his overnight address, while damage from Russia’s strikes on Ukrainian infrastructure continued to be felt. An accident at a critical power station that had been damaged by Russian attacks in the southern city of Odesa resulted in a citywide blackout, with no indication of when power would be restored.

“The situation is complex, the scale of the accident is significant, it is impossible to quickly restore power supply, in particular to critical infrastructure,” Ukraine’s prime minister, Denys Shmyhal, said in a statement. He said that generators were being raced to the city to try to reconnect critical infrastructure.

Despite the ongoing fighting, Russia and Ukraine said on Saturday that they had carried out another large-scale exchange of prisoners of war.

Andriy Yermak, the head of the Ukrainian president’s office, said that 116 Ukrainians had been released — including “defenders of Mariupol, Kherson partisans, snipers from Bakhmut vicinities, and other heroes.” The bodies of two British volunteers and a former member of the French Foreign Legion also were turned over by the Russians, he added. Russia’s Defense Ministry said in a statement that a “complicated negotiation” had led to the return of 63 Russian troops, including “sensitive category” prisoners whose release was facilitated by the United Arab Emirates.

The United Arab Emirates has tried to facilitate prisoner swaps between Russia and Ukraine over the course of the war. The government hosted the exchange of the W.N.B.A. star Brittney Griner for a Russian arms dealer, Viktor Bout, on the tarmac of an Abu Dhabi airport.

A Russian official reported a Ukrainian attack and subsequent fire Saturday at an industrial facility near the border. Vyacheslav V. Gladkov, the governor of the Belgorod region, wrote on Telegram that “projectiles hit the premises of an industrial plant.” In subsequent posts, he said that there were no casualties, as staff members were quickly evacuated.

Reporting was contributed by Natalia Yermak, Anastasia Kuznietsova, Ivan Nechepurenko and Cassandra Vinograd.