Fighting rages in battle for Ukraine's east

Street fighting between Ukrainian and Russian troops raged in the battle for the industrial city of Sievierodonetsk as Moscow's forces pushed to conquer Ukraine's eastern Donbas, seeking a decisive win more than 100 days into the invasion.

Which side had the upper hand was unclear, with "the situation changing from hour to hour," Oleksandr Stryuk, head of administration in Sievierodonetsk, said on television.

The city has become the main target of the Russian offensive in the Donbas - comprising Luhansk and Donetsk provinces - as the Kremlin's invasion grinds on in a war of attrition that has seen cities laid waste by artillery barrages.

"In the city, fierce street fighting continues," President Volodymyr Zelenskiy said in his nightly video address on Monday. "The Russian army is trying to deploy additional forces towards Donbas."

The province's governor Serhiy Gaidai said earlier on Monday the situation had worsened after Ukrainian defenders had pushed back the Russians over the weekend as they seemed close to victory.

Two civilians were killed in Russian shelling in the Donetsk and Luhansk regions on Monday and Russian forces had fired at more than 20 communities, according to the Ukrainian military. Russia denies targeting civilians in the conflict.

"We are offering people the chance to evacuate," Donetsk regional governor Pavlo Kyrylenko said on television.

"From Sloviansk we had more than 100 people evacuated since last week. About 24,000 residents remain. People are now understanding, though it is late, that it is time to leave."

After being pushed back from Kyiv and Kharkiv in the war's early stages, Russia says it is on a mission to "liberate" the Donbas, partly held by separatists since 2014, and is engaged in a "special military operation" to disarm and "denazify" its neighbour.

Ukraine and allies call this a baseless pretext for a war that has killed thousands, flattened cities and forced millions of people to flee abroad.