Russia called on Ukrainian soldiers in Severodonetsk to surrender after it blew up the last bridge into the city, trapping all those left behind in one of the bloodiest battlegrounds of the war.
Kyiv's forces were told to "stop their senseless resistance and lay down their arms" by Mikhail Mizintsev, the head of Russia's National Defence Management Centre.
Fighting in the industrial city that would give Russia total control of Luhansk, one half of the Donbas region, has raged door-to-door, with video from the front lines showing soldiers desperately firing at each other from close range.
Volodymyr Zelenskyy, the Ukrainian president, said the price of the battle was "terrifyingly high", describing it as one of the most brutal in European history.
With two of the bridges that cross from Severodonetsk into the neighbouring town of Lysychansk already destroyed, Ukraine had been relying on the only crossing left to ferry in supplies and evacuate civilians.
Serhiy Haidai, the governor of the Luhansk region, said humanitarian convoys came under shelling on about half of the crossings. Craters covered the bridge's asphalt, while burned-out vehicles partially blocked the road.
In one video from inside the city, Ukrainian troops were seen trying to escort an elderly woman with a broken, bloody arm to safety. In another, a woman repeatedly makes the sign of the cross under heavy shelling.
In his daily video update, Haidai said on Tuesday that Russia had not "completely captured" the strategically key city and insisted "part of the city" was still under Ukrainian control.
Moscow has used its "significant advantage in artillery" to launch ground assaults on the city centre, the local official said, adding Russian troops used the bombardment to push Ukrainian defenders out of the area.
"The Russians are destroying quarter after quarter," Haidai said, adding the Russian military had been "partially successful at night".
Some 15,000 civilians are thought to be stranded in Severodonetsk now with no escape west to the neighbouring city of Lysychansk, which is also being shelled but remains in Ukrainian hands.
The remaining residents are being forced to survive in "extremely difficult conditions", Haidai added.
In a separate post on the Telegram messaging app, Haidai said civilians had been forced to flee a "real hell" while under attack by constant Russian shelling.
He said escape routes were fraught with danger, with residents "running under fire to the car" and only able to move onward under the cover of darkness.
"The shelling is so powerful that people can no longer stand in the shelters," he wrote. "But we cannot lose as long as it is possible to save at least one life – we will save."
With no way out, there are mounting fears that Severodonetsk could develop into another Mariupol, the southern Ukrainian port left virtually razed after months of Russian bombardment.
Russian forces have almost constantly bombarded the sprawling Azot chemical plant, where 500 people, including 40 children, are sheltering in bunkers.
The attacks have thrown clouds of toxic chemicals, used to produce nitrogen fertilisers, into the atmosphere as conditions on the ground deteriorate.
Haidai said Ukrainian negotiators had so far failed in talks with Moscow to evacuate civilians from the chemical plant.
"We are trying to agree, with the help of Irina Vereshchuk [Ukraine's deputy prime minister], to organise a corridor," he said. "So far, it has been unsuccessful."
He added: "Azot's shelters are not as strong as in Mariupol's Azovstal, so we need to take people out with security guarantees."
Russia also offered to set up a humanitarian convoy to evacuate civilians sheltering in the Azot chemical plant.
On Tuesday, some of those who have escaped from the plant, which has deep bunkers and running water, told The Telegraph that heavy Russian shelling has caused dangerous leaks of ammonia gas.
The Siversky Donets river between Severodonetsk and Lysychansk is about 50m wide.
Oleksandr Stryuk, the mayor of Severodonetsk, said civilian evacuations would continue despite the bridge's destruction. He said they were being done "one by one, and every possible chance is taken".
Ukraine's soldiers have the advantage of high ground on the bank across the river from Severodonetsk, presenting a challenge to Russian troops if they seek to press on with their offensive.
The West has pledged more weapons to boost Ukraine's battle for the Donbas, but Kyiv said on Tuesday that the country had received just 10 per cent of the weapons it had requested.
"From what we said we need, we got about 10 per cent," said Anna Malyar, the deputy defence minister, adding that the West should speed up its delivery schedule.
"We need to know clear deadlines because every day there's a delay, we're talking about the lives of Ukrainian soldiers and civilians.
"We can't wait very long, because the situation is very complicated," she added, referring to the creeping Russian advance in Donbas.
In Britain, the Ministry of Defence this week said river crossings would be a crucial next phase of the war.
It said in a daily briefing: "Russia is either going to have to complete ambitious flanking actions, or conduct assault river crossings.
"Ukrainian forces have often managed to demolish bridges before they withdraw, while Russia has struggled to put in place the complex co-ordination necessary to conduct successful, large-scale river crossings under fire."