Ukrainians left with one way out of Sievierodonetsk as fierce fighting rages

Ukrainian defenders were fighting fiercely for "every metre" of Sievierodonetsk, President Volodymyr Zelenskiy said, as Russian forces destroyed a bridge to another city across the river, leaving stranded civilians with just one way out.

Russian forces have taken most of Sievierodonetsk, having pulverized parts of the city in one of the bloodiest assaults since they invaded Ukraine on February 24, and victory there could give them momentum in a wider battle for control over Ukraine's eastern Donbas region.

"The key tactical goal of the occupiers has not changed: they are pressing in Sievierodonetsk, severe fighting is ongoing there - literally for every metre," Ukrainian President Volodymyr Zelenskiy said in his nightly video address on Sunday, adding that Russia's military was trying to pour reserves into the Donbas.

Zelenskiy said the image of a 12-year-old wounded in a Russian strike was now the enduring worldwide face of Russia.

"These very facts will underscore the way in which Russia is seen by the world," he said.

"Not Peter the Great, not Lev Tolstoy, but children injured and killed in Russian attacks," he said, in an apparent reference to Russian President Vladimir Putin's remarks last week comparing Moscow's military campaign to Russian emperor Peter the Great's 18th century conquest of lands held by Sweden.

Ukrainian and Russian forces were still fighting street-by-street in Sievierodonetsk on Sunday, the governor of Luhansk province, Serhiy Gaidai, said.

Russian forces have taken most of the city but Ukrainian troops remain in control of an industrial area and the Azot chemical plant where hundreds of civilians are sheltering.

"About 500 civilians remain on the grounds of the Azot plant in Sievierodonetsk, 40 of them are children. Sometimes the military manages to evacuate someone," Gaidai said.

But the Russians had destroyed a bridge over the Siverskyi Donets River linking Sievierodonetsk with its twin city of Lysychansk, Gaidai said.

That left just one of three bridges still standing.

"If after new shelling the bridge collapses, the city will truly be cut off. There will be no way of leaving Sievierodonetsk in a vehicle," Gaidai said, noting the lack of a cease-fire agreement and no agreed evacuation corridors.

Gaidai said Lysychansk was also being shelled by Russian forces, and a six-year-old child had been killed there.

Reuters could not independently confirm that account.

In Pokrovsk, southwest of Sievierodonetsk, women, children and elderly, some in wheelchairs, boarded the only train evacuating people on Saturday, at the start of a long journey from the conflict zone to safety in Lviv near the border with Poland.