Ukrainian officials said forces had been forced to withdraw from the destroyed city to neighbouring Lysychansk, across the Seversky Donets river, where there are now reports of street-to-street fighting.
“The city [Severodonetsk] has been fully occupied by the Russians,” said Oleksandr Striuk, the head of the city’s military administration.
The fall of Severodonetsk is both a morale boost for the Kremlin and a strategically important conquest. It not only means that the Kremlin controls the largest cities in Luhansk, which makes up half Donbas, but also frees its armies to capture the industrial cities of Kramatorsk and Slovyansk further west.
Vladimir Putin had become increasingly frustrated that determined Ukrainian resistance had slowed his far larger army in Severodonetsk.
British intelligence reports said that, under pressure from Putin to speed up its conquest of Severodonetsk, the Russian army had fired shells designed to sink aircraft carriers at Ukrainian forces.
The focus of the battle for Severodonetsk over the past few weeks has been the Azot chemical plant, a sprawling site that provided a defensive position for its defenders similar to the Azov steelworks in Mariupol.
However, the Azot plant does not have the same extensive tunnel network and was also pockmarked with potential poisonous chemical stores, making it far harder to defend.
Quoting Russian army officers, a Russian news agency reported that the plant had now been captured. Ramzan Kadyrov, the Chechen leader, said the last 800 civilians sheltering in the site had left.
After the fall of Severodonetk, fighting in Lysychansk was intensifying, Andrei Marochko, a representative of pro-Russian separatists, said on his Telegram channel.
“The people’s militia of the Lugansk People’s Republic and the Russian army have entered the city of Lysychansk,” he said. “Street fighting is currently taking place.”
Russia appeared to be increasing its attacks elsewhere in Ukraine. Ukrainian military intelligence said 12 missiles had been fired by Russian fighter jets as they flew through Belarusian airspace at regions to the north of Kyiv, the Ukrainian capital.
Mykhailo Podolyak, an adviser to Volodymyr Zelensky, the Ukrainian president, said 48 missiles in total had been fired across the country, adding: “Russia is still trying to intimidate Ukraine, cause panic and make people be afraid.”