Russia’s spring offensive has stalled at Ukraine’s Fortress Belt — ISW says it won’t break through in 2026

Russia's spring-summer 2026 offensive is struggling to gain ground against the northern section of Ukraine's Fortress Belt in Donetsk Oblast, according to ISW. The think tank assessed that Russian forces remain unlikely to seize the fortified defensive line this year, with the only army positioned for a direct push on Sloviansk already stalled and flanking forces advancing even more slowly.

Russian 3rd Combined Arms Army stalls east of Sloviansk

Ukrainian military observer Kostyantyn Mashovets reported on 29 March that elements of the Russian 3rd Combined Arms Army fighting near Kryva Luka and Zakitne — east of Sloviansk, the northern anchor of the Fortress Belt — have made no progress since approximately 22 March. The army had achieved a tactical penetration of Ukrainian defenses between Kryva Luka and Riznykivka over the preceding month, since roughly 27 February, but that advance has now ground to a halt.

Mashovets assessed that elements of the 20th and 25th Combined Arms Armies in the Lyman direction and the 8th Combined Arms Army and 3rd Army Corps in the Kostiantynivka direction are all advancing more slowly than the 3rd CAA. He concluded that only the 3rd CAA is positioned to drive directly on the Sloviansk-Kramatorsk agglomeration. ISW assessed that attempting such an operation without mutually supportive flanking advances would likely inflict critically high casualties for disproportionately minimal gains.

Russia's strategic dilemma: push forward or reinforce flanks

Mashovets noted that elements of the 3rd CAA could be diverted to support Russian operations toward Lyman or Kostiantynivka rather than continuing a direct push against the Fortress Belt. Such a diversion would require Russia to temporarily abandon its offensive on the northern section of the fortified line — a move that would undermine the Kremlin's information warfare effort portraying Russian forces as advancing simultaneously across the entire theater and Ukrainian defenses as collapsing.

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ISW: Russia has likely begun its anticipated spring-summer 2026 offensive against Ukraine’s Fortress Belt in Donetsk Oblast

Ukrainian Joint Forces Task Force Spokesperson Colonel Viktor Trehubov assessed on 28 March that Russian forces toward Lyman are likely waiting for spring foliage to emerge, which would provide concealment for assaults and infiltration missions.

"Russian forces remain unlikely to seize Ukraine’s Fortress Belt in 2026, especially if many of the forces involved in such an operation are bogged down in Ukrainian defenses," ISW concluded.