KYIV, June 13 — Russian troops swarmed into Sievierodonetsk, as their artillery pounded parts of the city where Ukrainian defenders mounted a desperate rearguard action in the fiercest fighting of a wider battle for control over Ukraine’s eastern Donbas region.

The Russian destruction of a bridge left stranded civilians with just one remaining bridge to escape across a river to the neighbouring city of Lysychansk, which was also being shelled but was still in Ukrainian hands.

Hundreds of civilians in Sievierodonetsk were sheltering in the city’s Azot chemical plant, creating a scenario similar to the fall of the southern port city of Mariupol, where hundreds of people were trapped for weeks in the Azovstal steelworks.

"Russians continue to storm the city, having a significant advantage in artillery they have somewhat pushed back the Ukrainian soldiers,” said Serhiy Gaidai, governor of the Luhansk region.

"The Russians are destroying quarter after quarter,” Gaidai said today.

Russian forces have taken most of Sievierodonetsk, having pulverised parts of the city in one of the bloodiest assaults since they invaded Ukraine on February 24.

Ukrainian President Volodymyr Zelenskiy said in his nightly video address yesterday that Russia was trying to pour military reserves into the Donbas.

"The key tactical goal of the occupiers has not changed: they are pressing in Sievierodonetsk, severe fighting is ongoing there — literally for every metre,” Zelenskiy said.

Zelenskiy said attacks that resulted in child casualties had created a lasting image of Russia for the rest of the world.

"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.

Russia has denied targeting civilians.

Putin launched what he called a "special operation” to restore Russian security and "denazify” its southern neighbour. Ukraine and its Western allies call this a baseless pretext for a war which has raised fears of wider conflict in Europe.

In the biggest assault on a European country since World War Two, more than five million people have fled Ukraine, thousands have died and cities left in rubble. The war has sparked a global energy and food crisis by disrupting gas, oil and grain supplies from Russia and Ukraine.

Trapped in chemical plant

After failing to take the capital Kyiv, Moscow turned its attention to expanding control in the Donbas, where pro-Russian separatists have held territory since 2014.

In Sievierodonetsk, the last pocket of Ukrainian land held in the strategic Luhansk region, Ukrainian troops were fighting street by street to hold onto the city, with both Ukrainian and Russian forces suffering heavy losses, Roman Vlasenko, head of Sievierodonetsk district administration, told local TV.

"Our boys are holding on but the conditions are tough,” he said. Vlasenko said the city had been without communications and normal services for a month.

Russian shelling had hit the Azot chemical plant area three times, said Luhansk governor Gaidai.

"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,” he said.

The destruction of a bridge over the Siverskyi Donets River linking Sievierodonetsk to Lysychansk has left just one of three bridges still standing, he said.

"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 or agreement on 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, south-west 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.

"We held on until the last moment, we didn’t want to leave, but life has forced us to survive,” Lyuba, a woman from Lysychansk, told Reuters Television as she waited for the train to depart. "We are leaving, we don’t know where, to whom, but we are leaving.”

Arms supplies requested

In Western Ukraine, Russian cruise missiles destroyed a large depot containing US and European weapons in the Ternopil region, Russia’s Interfax agency reported.

Ternopil’s governor said rockets fired from the Black Sea at the city of Chortkiv had partly destroyed a military facility and injured 22 people. A local official said there were no weapons stored there.

Reuters could not independently confirm the differing accounts.

Yesterday, the Ukrainian general staff said on Facebook that General Valeriy Zaluzhny, the head of Ukraine’s armed forces, had spoken to General Mark Milley, the top US military officer, and reiterated a request for more heavy artillery systems.

Moscow has criticised the United States and other nations for sending Ukraine weapons, threatening to strike new targets if the West supplied long-range missiles. — Reuters