Russian troop build-up threatens Ukraine's hold on strategic Donbas gateway

Russian forces have intensified operations around the eastern Ukrainian city of Kostyantynivka, with Ukrainian soldiers and military observers warning that Moscow is attempting to surround the strategic urban centre in a move that could bring it closer to achieving one of its key objectives in the war — full control of the Donbas region.

Kostyantynivka is regarded as a gateway to the remaining Ukrainian strongholds in eastern Ukraine, including Kramatorsk and Sloviansk. Its fall would significantly complicate Kyiv's defensive position in Donetsk region and open new avenues for Russian advances.

Ukrainian soldiers operating in the area told the BBC that Russian troops have infiltrated parts of the city and established positions in several locations.

“The entire city is effectively becoming a grey zone,” one Ukrainian drone pilot said, describing a situation in which neither side exercises complete control over large sections of the urban area.

Russian forces have reportedly advanced from the south and have also been detected near the northern outskirts of the city.

Moscow has claimed that its troops are making rapid gains in the south-western sector of Kostyantynivka and have encircled Ukrainian units. Ukrainian military authorities reject those claims.

Brigadier General Oleksandr Bakulin, commander of Ukraine's 19th Corps, said the situation remained under control and insisted Russian forces had achieved no significant breakthrough. However, he acknowledged that around 130 Russian soldiers were operating inside the city.

A Ukrainian officer deployed in Kostyantynivka said Russian forces continued to accumulate troops despite ongoing Ukrainian efforts to clear infiltrated areas.

According to Ukrainian soldiers, Russia has adapted its tactics by targeting Ukrainian drone operators and launch sites, reducing Kyiv's ability to monitor and strike advancing infantry units.

While Ukrainian drones have played a central role in slowing Russian advances throughout the war, soldiers said Russian forces were increasingly relying on artillery, multiple-launch rocket systems and military aviation to suppress Ukrainian positions.

Strategic battle for Donbas

Military analysts say Russia is employing tactics similar to those used during operations around Pokrovsk and other eastern Ukrainian cities, advancing along the flanks to threaten supply routes and gradually isolate urban centres.

Recent Russian claims of capturing villages west of Kostyantynivka suggest an effort to tighten the encirclement of the city and disrupt Ukrainian logistics.

The battle comes as Ukraine continues long-range strikes against Russian energy infrastructure and supply routes, including attacks on oil refineries and transport links supporting Russian operations.

Some Ukrainian military personnel warned that maintaining supply lines into Kostyantynivka was becoming increasingly difficult because of constant Russian attacks and drone surveillance.

The Ukrainian frontline monitoring project DeepState described the situation as critical and warned that the fall of Kostyantynivka would further complicate logistics across eastern Ukraine and increase pressure on nearby cities, including Kramatorsk.

Despite the growing challenges, Ukrainian troops continue to defend positions inside the city, although some soldiers have expressed concerns about manpower shortages and difficulties replacing battlefield losses.

For now, fighting continues inside and around Kostyantynivka, with both sides viewing control of the city as crucial to the next phase of the war in eastern Ukraine.