Jens Asbjørn Bøgen
One of the most important defensive corridors is likely to see some of the heaviest fighting of the year.
The war in Ukraine has lasted for nearly four years now, and Russian losses continue to be sky-high.
According to estimates from Ukraine’s General Staff, the Russian army lost more than 410,000 troops in 2025, down slightly from an estimated 431,000 losses in 2024, but significantly higher than in 2023 (253,000) and 2022 (106,000).
Russian losses are likely to increase further in 2026, as Russian offensives are now reaching Ukraine’s Fortress Belt.
Note that the figures from Ukraine’s General Staff have not been independently verified.
What is the Fortress Belt?
In August 2025, Ukraine’s Fortress Belt was described by the Institute for the Study of War (ISW) as a 50-kilometer (31-mile) fortified defensive corridor anchored by several cities and towns in western Donetsk Oblast.
For the past 11 years (since the Russian annexation of Crimea), Ukraine has invested heavily in reinforcing the belt, creating a large defense industry and improving and expanding the defensive infrastructure in the area.
In the northern half of the belt, the cities of Slovyansk and Kramatorsk serve as important logistical hubs, while in the south, Druzhkivka, Oleksiyevo-Druzhkivka, and Kostyantynivka make up the rest of the belt.
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Why is it so important?
The belt acts as an important logistical hub for Ukrainian forces in the defense of the rest of Donetsk Oblast, especially during the battle for Pokrovsk, which lies just southwest of the belt.
If the Fortress Belt were to fall, it would make it much more difficult for Ukraine to defend against ongoing Russian attacks and would also “open the road” for Russia to push further into Ukraine.
Why Putin is expected to push even harder
Vladimir Putin has repeatedly demanded the full withdrawal of Ukrainian troops from Donetsk Oblast, including the Fortress Belt.
ISW has previously assessed that Russian troops are attempting to envelop the Fortress Belt from both the north and the south, which could also explain why Russia is investing so heavily in taking Pokrovsk.
Donetsk Oblast is also part of the so-called Donbas region, an important industrial area in eastern Ukraine. Putin said in early December: “Either we liberate these territories by force, or Ukrainian troops will leave these territories.”
Analysts have previously suggested that Putin is gambling on gaining additional battlefield momentum in order to force Ukraine into signing a peace deal favoring Russian demands.
But as Ukraine has spent 11 years fortifying the belt, Russia’s expected attempt at taking the Fortress Belt will likely result in increasing losses – and very possibly higher numbers than we have seen over the past two years.
Sources: Institute for the Study of War (ISW), Ukraine’s General Staff, Reuters, BBC, India Today
