Moscow said it had opened a humanitarian corridor from the plant on Wednesday to allow civilians to escape to Russian-controlled territory. It accused Ukrainian troops of violating the ceasefire and effectively using civilians as human shields.

“There are no obstacles for civilians to leave … except for the decision in principle by the Kyiv authorities themselves,” the ministry said in a statement.

Ukraine has denied Russian claims that it uses civilians as human shields.

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Many previously announced planned evacuations from other areas of fighting in Ukraine have failed, with each side blaming the other. Some Ukrainians have been reluctant to evacuate to Russian-held territory.

Rodion Miroshnik, an official in the Russian-backed self-styled separatist administration of the Luhansk People’s Republic, said that Ukrainian forces in the plant numbered up to 2,000 people.

Ukraine says the number of civilians at the plant is closer to 500, and that around 10,000 civilians remained in the city. Sievierodonetsk’s population was about 100,000 before the war.

Luhansk is one of two eastern provinces Moscow claims on behalf of separatist proxies. Together they make up the Donbas, an industrial region where Russia has focused its assault after failing to take Ukraine’s capital Kyiv in March.

Capturing Sievierodonetsk has become a key goal, as it would open the road to Sloviansk and another major city, Kramatorsk.

Kyiv’s forces face an increasingly desperate situation in Sievierodonetsk, with Ukrainian authorities estimating the Russians now control up to 80 per cent of the city as they seek to encircle it. The city is largely in ruins.

The Ukrainian governor of Luhansk, Serhiy Gaidai, told Associated Press that the situation in the city was getting worse because Russian forces have more manpower and weapons.

“But our military is holding back the enemy from three sides at once,” Gaidai said. “The enemy is advancing because of significant advantage in artillery and people, but the Ukrainian army is holding on to its positions in the city.”

He said Ukraine’s army was also trying to stop Russian forces from taking Sievierodonetsk’s twin city Lysychansk on the opposite bank of the Siverskyi Donets river.

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President Vladimir Putin has repeatedly said that the main immediate reason for what he casts as a “special military operation” was to protect the Russian-speakers of Donbas from persecution and attack.

But Dmitry Medvedev, the deputy chair of Russia’s Security Council who is a former Russian president, ominously suggested that Russia appears intent on not just claiming some territory but eliminating Ukraine as a nation.

In a Telegram post, he wrote that he saw reports in which Ukraine wants to receive liquefied natural gas from its “overseas masters” with payment due in two years.

He added: “But there’s a question. Who said that in two years Ukraine will even exist on the map?”

Mykhailo Podolyak, an adviser to Ukriane President Volodymyr Zelensky reacted to Medvedev’s comments.

“Ukraine has been and will be. Where will Medvedev be in two years, that’s the question,” Podolyak said on Twitter.

Additional reporting by Associated Press and Agence France-Presse