Russian soldiers in the city, advancing from the south, have been seen in the northern outskirts of Kostyantynivka.
Adopting a similar strategy to that used to capture Pokrovsk in 2025, troops have begun advancing along the flanks to surround the city and cut off supply routes.
Last month, reports citing Ukrainian intelligence claimed Russia’s top commanders had convinced Russian President Vladimir Putin they could seize Kramatorsk and Slovyansk, the towns at the centre of the fortress, by the end of the year.
Such a breakthrough would bring the Kremlin closer to achieving one of its most significant remaining war aims: the conquest of the entire Donbas region.
Kyiv, however, has rejected claims that Kostyantynivka is being surrounded. Brigadier General Oleksandr Bakulin, commander of Ukraine’s 19th Corps, insisted that “the situation remains under control” and “the enemy has no success”.
The commander nevertheless acknowledged that around 130 Russian soldiers were currently operating inside the city.
According to the most recent figures released by authorities, around 2000 civilians remain in Kostyantynivka, which has been cut off from all emergency and humanitarian services.
Ukraine’s fortress belt is a strategically important 50km defensive line stretching across northern Donetsk Oblast. It forms the backbone of the country’s eastern defences. It comprises four key cities Russia has failed to capture: Slovyansk, Kramatorsk, Druzhkivka and Kostyantynivka.
Although the Kremlin has repeatedly launched offensives against the area, the Institute for the Study of War estimates that, at Russia’s current rate of advance, conquering the remainder of Donetsk Oblast could take at least two years.
Moscow has therefore sought to increase pressure on Kyiv during negotiations, demanding control of territory it has yet to seize on the battlefield. However, Ukrainian President Volodymyr Zelenskyy has rejected demands to give up the fortress belt, bound by constitutional limits, strategic realities and the will of his people.
Dr Shane O’Rourke, an expert in Russian history at the University of York, described Kostyantynivka as being “in balance”, adding that if Putin captured the rest of Donetsk, it “will give him a spurious claim to some sort of victory”.
He told the Daily Telegraph: “It does seem that the city is in the balance at the moment, but we have been here before with many other cities. The Russians have a habit of claiming cities have fallen long before they have and in some cases it has become almost a ritual.
“If it falls, it will be a loss, but I don’t think it will be the end of the fortress belt. The taking of all of Donetsk is about all that’s left of Russia’s original war aims from 2022. Putin is desperate for that. It will give him a spurious claim to some sort of victory. That still leaves the other fortress cities.”
Russia’s infiltration of Kostyantynivka comes as Russia’s full-scale war in Ukraine enters a period of relative stagnation along much of the front.
After a Ukrainian drone attack on Moscow’s oil refinery last week, Russia pulled an air-defence system from the front line and moved it to Moscow to defend the Russian capital. Ukrainian commanders claim their forces are recapturing more territory this year than they are losing.
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