The authorities of several regions have also reported having been targeted by intense Russian bombardments, in the north and west of the country, but also in a more southern city.
This Ukrainian withdrawal is a step towards taking control of the entire province of Luhansk, leaving kyiv forces only the city of Lysytchansk.
The Russian army has set itself the goal of seizing the entire territory of the provinces of Luhansk and Donetsk, partly controlled by pro-Russian separatists since 2014, and which both form the Donbass region.
“The city is now totally occupied by Russia. From what I have been told, they have appointed some sort of commander,” Oleksander Striouk, the city’s mayor, told national television.
The battle for Sievierodonetsk – a city that had nearly 100,000 inhabitants before the war – became the epicenter of the fighting for control of Donbass, the main objective that Moscow set itself after giving up the capture of kyiv in the first weeks of its invasion operation, launched on 24 February.
After Sievierodonetsk, other big battles could follow in the Donbass. According to Ukraine, Russia is massing troops to attack Sloviansk from the north and along a front near Bakhmut in the south of the region.
The Ukrainian authorities hope that by concentrating its efforts on Donbass, the Russian army will empty other fronts and expose itself to counter-attacks, as last month when the Ukrainian forces were able to reconquer territories around Kharkiv, in the northeast of the country.