Russian forces swarmed into the eastern Ukrainian city of Severodonetsk and pounded a zone where hundreds of civilians were sheltering, a Ukrainian official said Monday, a scene that mirrored Moscow's brutal capture of Mariupol last month.

Ukraine has issued increasingly urgent calls for more Western weapons to help defend Severodonetsk, which Kyiv says could hold the key to the outcome of the battle for control of the eastern Donbass region and the future course of the war.

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

Russia's Defense Ministry said Monday its missiles had destroyed a large quantity of weapons and military equipment in the Donbass region, including some that had been sent by the United States and European nations. The ministry also said high-precision air-based missiles had struck near the Udachne railway station, hitting equipment that had been delivered to Ukrainian forces.

Meanwhile, in a report that was not confirmed by the Ukrainian side, a Russian-backed separatist said the last bridge into the city had been destroyed on Sunday, effectively blockading its Ukrainian defenders inside.

"They have two options: either follow the example of their fellow soldiers and surrender, or die," Russia's RIA news agency quoted separatist spokesperson Eduard Basurin as saying. "They have no other option."

Regional governor Sergei Gadai had said on Sunday evening the last crossing over the Donets River was still standing after another bridge was destroyed earlier in the day.

"The third bridge is working. But the condition of the bridge is threatening: it is half-destroyed, it is impossible for trucks to move on it," he said.

On Monday he said fighting was raging in the city, where Ukrainian forces were defending building by building.

"The battles are so fierce that fighting for not just a street but for a single high-rise building can last for days," he said on social media.

Russian artillery fire also rained down on the Azot chemical plant, where hundreds of civilians were sheltering, said Gaidai, governor of the Luhansk region in eastern Ukraine that includes Severodonetsk.

Before Mariupol fell to Russia last month, hundreds of civilians and badly wounded Ukrainian soldiers were trapped for weeks in the Azovstal steelworks. Ukrainian officials say cholera is now spreading among remaining residents due to bodies buried in rubble from destroyed residential buildings.

Gaidai estimated that Russian forces now controlled about 70% of Severodonetsk, and said they were destroying it "quarter by quarter" in one of the bloodiest assaults since the invasion was launched on Feb. 24.

"Russians continue to storm the city, having a significant advantage in artillery they have somewhat pushed back the Ukrainian soldiers," Gaidai said on Monday.

Image of Russia

Ukrainian President Volodymyr Zelenskyy said in his nightly video address on Sunday that Russia was trying to pour military reserves into Donbass.

"The key tactical goal of the occupiers has not changed: they are pressing in Severodonetsk, severe fighting is ongoing there – literally for every meter," Zelenskyy said Sunday. Zelenskyy also said attacks that resulted in child casualties had created a lasting image of Russia in the eyes of the rest of the world, rather than the images Moscow was trying to project.

"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 neighbor. Ukraine and its Western allies call this a baseless pretext for an invasion that has raised fears of wider conflict in Europe.

More than5 million people have fled Ukraine, thousands have died and cities have been reduced to rubble in the biggest assault on a European country since World War II.

The war has sparked a global energy and food crisis by disrupting gas, oil and grain supplies from Russia and Ukraine.

Trapped in plant

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

In Severodonetsk, the last pocket of Ukrainian land held in the Luhansk region, Ukrainian and Russian forces were both suffering heavy losses, Roman Vlasenko, head of Severodonetsk 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 Severodonetsk, 40 of them are children. Sometimes the military manages to evacuate someone," he said, adding that the remaining bridge out of the city to the west was vulnerable.

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

Gaidai said the twin city of Lysychansk across the river to the west was also being shelled by Russian forces, and a 6-year-old child had been killed there.

Reuters could not independently confirm that account.

In Pokrovsk, southwest of Severodonetsk, women, children and elderly, some in wheelchairs, boarded the only train evacuating people on Saturday from the conflict zone to relative safety in faraway 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."

On Sunday, the Ukrainian general staff said Gen. Valeriy Zaluzhny, the head of Ukraine's armed forces, had spoken to Gen. Mark Milley, the top U.S. military officer, and reiterated a request for more heavy artillery systems.

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