Russia pounds on the gates of Ukraine's 'fortress belt'

Highlights:

• Kremlin troops converge on Kostiantynivka
• City anchors 'fortress belt' of key eastern cities
• Russian gains come even as Kremlin's war machine strained

Russia is grinding its way into Kostiantynivka, a key stronghold in Ukraine's eastern "fortress belt" long coveted by the Kremlin, even as its gains across the rest of the 1,200-km front line have largely stalled.

Fighting has begun to seep into the city itself. Small groups of Russian soldiers are attempting to infiltrate its outskirts, senior Ukrainian commanders said last week, suggesting close-quarters assaults could follow.

Kostiantynivka is the southernmost of four key settlements forming a defensive line central to Ukraine's effort to hold the heavily industrialised Donetsk region.

The push towards it underscores Moscow's enduring manpower advantage, even as Ukrainian mid-range drone strikes on logistics have weakened its fighting capabilities, analysts said.

"The effect (of mid-range strikes) hasn't been so great that it would have forced the Russians to suspend their offensive," said Emil Kastehelmi of the Black Bird conflict analysis team in Finland.

"So even though Russia has been taking increasingly heavy losses in the rear, they are still able to continue their offensives, at least in certain sectors."

Occupying Kostiantynivka would provide Russian forces a foothold from which to move north along the belt, now the central axis of their campaign.

But any advance would likely be long and bloody for its forces, in a possible echo of other costly sieges of eastern cities like Pokrovsk and Avdiivka.

President Vladimir Putin has insisted Russia must control all of Donetsk before the war ends. Ukraine still holds around a fifth of the region after more than four years of fighting.

'Stakes rising each day'

Putin said last week Russia was close to capturing Kostiantynivka, whose pre-war population of nearly 70,000 has fallen to around 2,000.

In comments to Ukrainian media, senior commanders of Kyiv's 19th Army Corps dismissed that claim as an exaggeration and said their troops were picking off small groups of Russians that had managed to enter.

Maj. Gen. Viktor Nikoliuk, the head of Ukraine's eastern operational command, told Ukraine's public broadcaster on Thursday that Kostiantynivka could hold out at the current rate of manpower and resources.

While the tactical situation is worsening for Ukraine, the Russian infiltrations are not enough for "a rapid operational breakthrough", the US-based Institute for the Study of War said in a 23 June assessment.

Still, Russian efforts to envelop the city through pincer movements are steadily raising the cost for Kyiv of defending it, said Ukrainian analyst Ruslan Mykula, of the DeepState open-source mapping group.

"A choice will have to be made: either raise the stakes or withdraw," he said. "And right now, the situation is such that the stakes are rising with each passing day."

Kastehelmi said the city's fall "seems to be more of a question of time".

Moscow's troops are also encroaching on the northern end of the fortress belt, threatening the cities of Sloviansk and Kramatorsk with frequent air and drone attacks from around 15 km (9 miles) away.

Ukrainian supply routes are already under sustained pressure, with artillery, drones and guided bombs battering infrastructure along the road north from Kostiantynivka, troops in the area said.

Drone-infested skies

Reuters recently joined members of the "Predator" rifle brigade under the National Police, assigned to patrol the embattled route against drones and remotely dropped mines.

Strands of fibre-optic cable, used to guide first-person-view drones, are strewn across anti-drone netting draped over the road, glistening under the scorching sun.

Ground robots carrying food, water and supplies – now the predominant method of delivery inside the so-called "kill zone" – trundle back and forth, as soldiers speed past on quad bikes.

The route is too dangerous to evacuate the dead and wounded on standard vehicles, said 34-year-old serviceman Oleksandr Kosmin: "Everything happens on foot."

Civilian life nearby is collapsing under the pressure. In Druzhkivka, around 12 km north, residents are being forced to leave as the fighting edges closer.

On one leafy street, a husband and wife were slumped, dead, inside a van struck by a Russian drone. White ribbons, meant to mark the vehicle as civilian, still fluttered on its roof.

"Why am I leaving? Because I'm scared. Drones are flying," said Larysa Sereda, 59, speaking from a police evacuation van.

"But I plan to return home. I don't want to stay in some strange place. The war will end, and I'll come home."

Russia's war machine stumbling

The creeping Russian gains around Kostiantynivka come despite mounting strains on its war effort caused by Ukrainian attacks on supply lines to and from Crimea, as well as longer-range strikes on the oil sector.

Russian-installed authorities on the occupied Black Sea peninsula have imposed a state of emergency to deal with economic issues and have halted all fuel sales to individuals and businesses.

On the battlefield more broadly, Russian forces appear overextended and frontline assaults often amount to just one or two soldiers, said Mykula, the Ukrainian analyst.

In comments to Reuters, however, Denis Pushilin, the Kremlin-installed head of Ukraine's eastern Donetsk region, said Russia's campaign to capture more cities was continuing.

"Talking about whether this is happening slowly or quickly isn't really the point," he said.

Russian hardliners have urged Putin to abandon the US-backed peace process and escalate his war as Ukraine's strikes intensify, including in Moscow.