Ukrainian forces may need to withdraw from Syevyerodonetsk, one of the two main cities in the last remaining pocket of resistance in the east that Russian forces are close to surrounding, an official there warned, as Britain said Moscow was in acute need of a victory in the Donbas region as political justification for the war.

Ukrainian President Volodymyr Zelenskiy called the current situation in Donbas “very difficult.”

“Russian forces have concentrated their efforts in the Donbas, using maximum artillery fire and missile strikes as Ukrainian forces protect our land in the way that our current defense resources allow,” Zelenskiy said in his nightly video address.

Russian troops seeking to regain momentum in the three-month-long war have been pressing a rapid advance in the Luhansk region with a focus on the cities of Syevyerodonetsk and Lysychansk.

The relentless and indiscriminate Russian artillery fire has destroyed Syevyerodonetsk almost completely and killed hundreds of civilians, officials there said.

Serhiy Hayday, the governor of Luhansk, said on May 28 that he estimates there are some 10,000 Russian troops in the region and that Russians are already in parts of Syevyerodonetsk.

“It is possible that in order not to be surrounded, they (Ukrainians) will have to leave,” Hayday said the previous night.

Syevyerodonetsk Mayor Oleksandr Stryuk said that at least 1,500 people have been killed in his city since the start of Russia’s invasion in late February. About 12,000 to 13,000 remain in the city — down from a prewar population of about 100,000, he said.

The British Defense Ministry said in its daily intelligence bulletin on May 28 that Russian forces had likely captured most of Lyman, a railway hub west of Syevyerodonetsk, in what appears to be a preliminary operation for the next stage of Russia’s offensive.

Ukraine said Russians had captured most of Lyman but that its forces were blocking their advance to the southwest.

The British intelligence report estimated that Russia is likely to prioritize forcing a crossing of the Siverskiy Donets River that separates Syevyerodonetsk from it twin city, Lysychansk.