Ukrainian forces may have to retreat from the Luhansk region to avoid being captured, a Ukrainian official has said, in what would be a major blow to efforts to repel Vladimir Putin's forces.
Russian troops have reportedly advanced in the east, where a focus on the Donbas region has shifted the momentum of the three-month-old war.
A withdrawal could bring bloodthirst Putin close to capturing eastern Ukraine's Luhansk and Donetsk regions and land a significant and symbolic blow onVolodymyr Zelenskyy's hero defenders.
His troops have gained ground in two areas, collectively known as the Donbas, while blasting some towns to wastelands.
Serhiy Gaidai, Luhansk's governor, said Russian troops had entered Sievierodonetsk, the largest Donbas city still held by Ukraine, after trying to trap Ukrainian forces there for days.
But he added Russian forces would not be able to capture the Luhansk region "as analysts have predicted".
"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," Gaidai said on Telegram.
He said 90% of buildings in Sievierodonetsk were damaged with 14 high-rises destroyed in the latest shelling.
Speaking to Ukrainian television, Gaidai said there were 10,000 Russian troops based in the region and they were "attempting to make gains in any direction they can".
He claimed several dozen medical staff were staying on in Sievierodonetsk. but that they faced difficulty just getting to hospitals because of the shelling.
President Volodymyr Zelensky said Ukraine was protecting its land "as much as our current defence resources allow".
Ukraine's military insisted 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.
'The General Staff of Ukraine's armed forces said on Saturday Ukrainian forces had repelled eight assaults in the Donetsk and Luhansk regions in the previous 24 hours.
Russia's attacks included artillery assaults in the Sievierodonetsk area "with no success", it claimed.
Analysts at the Institute for the Study of War, a Washington-based think tank, said while Russian forces had begun direct assaults on Sievierodonetsk, they would struggle in the city itself.
"Russian forces have performed poorly in operations in built-up urban terrain throughout the war," they said.
Enemy troops advanced after piercing Ukrainian lines last week in the city of Popasna, south of Sievierodonetsk.
The invaders' forces have captured several villages northwest of Popasna, Britain's defence ministry said.
Popasna was said to be in ruins.
The bloated body of a dead man in combat uniform could be seen lying in a courtyard when reporters visited the scorched area.
Resident Natalia Kovalenko had left the cellar where she was sheltering in the wreckage of her flat, its windows and balcony blasted away.
She said a shell hit the courtyard, killing two people and wounding eight.
"We are tired of being so scared," she said.
Russia's eastern gains follow the withdrawal of its forces from approaches to the capital, Kyiv, and a Ukrainian counter-offensive that pushed its forces from Kharkiv.
Forces shelled parts of Kharkiv on Thursday for the first time in days killing nine people, authorities said.
The Kremlin, however, denies targeting civilians in what it calls its "special military operation".
Ukraine's General Staff claimed on Saturday while there was no new attack on the city, there were multiple Russian strikes on nearby communities and infrastructure.
In the south, where Moscow has seized a swath of territory since the invasion, including the port of Mariupol, Ukrainian officials say Russia aims to impose permanent rule.
