Ukraine Retakes Kostiantynivka Positions as Russia Fires 135 Drones

For Serbia, a country balancing energetically and diplomatically between Brussels and Moscow, every shift on Ukraine’s eastern front is not an abstract dispatch from a distant battlefield but a variable that shapes the price of gas, the tone of the sanctions regime, and Belgrade’s room to maneuver. That is why the Institute for the Study of War (ISW) assessment for June 23 matters: in Kostiantynivka, the city Moscow has designated as the centerpiece of its spring-summer offensive, Ukrainian forces retook several lost positions, while only 100 to 150 Russian troops actually entered the city.

That figure reframes the picture. It describes the infiltration of small groups, not a broken and entrenched line that would allow the systematic capture of the urban core. Kostiantynivka anchors the Kramatorsk-Kostiantynivka defensive belt, which military analysts have long described as the backbone of Ukraine’s defense in Donetsk region. A collapse of that belt would open the road to Kramatorsk and Sloviansk, so every Russian step toward the city center carries weight far beyond its size.

Why is the offensive failing to deliver its promised breakthrough?

Moscow billed this campaign as decisive, but the result on the ground lags well behind the rhetoric. Instead of consolidated advances, the Russian army relies on inserting small infantry groups that Ukrainian forces then break up or push back. The estimate that no more than 150 troops entered the city points to attrition rather than momentum, and it explains why the front line is measured in streets rather than kilometers.

In parallel, Russia has intensified its air pressure. Overnight on June 23 it launched 135 drones at targets across Ukraine, continuing a pattern of grinding attacks on infrastructure and populated areas far from the line of contact. Such strikes do not move the front, but they wear down Ukrainian air defenses and signal that the Kremlin will not ease the pressure even as its ground offensive falters.

Ukraine’s answer increasingly lies not on the front but deep inside Russian territory. Its campaign of strikes on refineries and export infrastructure has, over the course of 2026, knocked out a significant share of Russia’s refining capacity, complicating the fuel supply that powers the offensive itself. It is a strategic choice: hit the machinery of war where it is more vulnerable than the fortified cities.

What does this mean for the negotiating table?

Military balance always spills over into diplomacy. The Kremlin expects the imminent return of envoys Steve Witkoff and Jared Kushner to Moscow, signaling that mediation continues alongside the fighting. The outcome around Kostiantynivka directly feeds those talks: if the city holds, Kyiv arrives at the table arguing that the Russian offensive lacks the capacity for a decisive breakthrough, while its fall would hand Moscow a card to raise the stakes.

For Belgrade and the wider region, the meaning is measurable. A prolonged stalemate in eastern Ukraine keeps Serbia’s European prospects and the sanctions question in a state of permanent uncertainty, while any sudden reversal on the ground would accelerate pressure to align foreign policy. The geopolitical reality is that the fate of a single city in Donetsk region is read in Brussels and in Belgrade’s offices alike.

Can a small town in Donbas overturn the entire logic of the war, or is its defense just one more point in a grinding conflict without a winner?