Ukrainian forces may have to retreat from their last pocket in the Luhansk region to avoid being captured, a Ukrainian official said, as Russian troops press an advance in the east that has shifted the momentum of the three-month-old war.

A withdrawal could bring Russian President Vladimir Putin closer to his goal of capturing eastern Ukraine’s Luhansk and Donetsk regions in full. His troops have gained ground in the two areas collectively known as the Donbas while blasting some towns to wastelands.

Luhansk’s governor, Serhiy Gaidai, said Russian troops had entered Sievierodonetsk, the largest Donbas city still held by Ukraine, after trying to trap Ukrainian forces there for days. Gaidai said 90% of buildings in the town were damaged.

“The Russians will not be able to capture Luhansk region in the coming days as analysts have predicted,” Gaidai said on Telegram, referring to Sievierodonetsk and its twin city Lysychansk across the Siverskiy Donets River.

“We will have enough strength and resources to defend ourselves. However it is possible that in order not to be surrounded we will have to retreat.”

Russia’s separatist proxies said they now controlled Lyman, a railway hub west of Sievierodonetsk. Ukraine said Russia had captured most of Lyman but that its forces were blocking an advance to Sloviansk, to the southwest.

President Volodymyr Zelensky  said Ukraine was protecting its land “as much as our current defence resources allow”. Ukraine’s military said it had repelled eight attacks in Donetsk and Luhansk on Friday, destroying tanks and armoured vehicles.

“If the occupiers think that Lyman and Sievierodonetsk will be theirs, they are wrong. Donbas will be Ukrainian,” Zelensky  said in an address.