Ukrainian forces have derailed Russia’s plan to encircle and occupy the remaining Ukrainian-controlled territory of the Donetsk region this year, the Washington-based think tank Institute for the Study of War (ISW) concluded in an assessment based primarily on open-source intelligence.

The Russian campaign centred on a deep pincer movement targeting what the report calls the “fortress belt” — a defensive and logistical network protecting the Ukrainian-held portion of the Donbas — advancing from Lyman in the north and Dobropillia in the south-west, with both arms intended to link up near Barvinkove in the Kharkiv region.

Completing such an encirclement would have gone a long way towards Moscow’s longstanding objective of occupying all of Donetsk region and would have given the Kremlin something to show Russian society for the costs of the war.

Ukraine foils Russian offensive in Donetsk Ukraine’s counter-offensive on the Lyman axis, dubbed Operation Vivaldi, dismantled the northern arm of that pincer.

Ukrainian forces advanced along the Ridkodub–Nove–Novomykhailivka line in the north and the Yarova–Drobysheve–Stavky line in the south, collapsing the salient Russia had built to threaten Sloviansk from the north-east and forcing Russian units onto the defensive.

Commander of Ukraine’s 3rd Army Corps Andrii Biletskyi said the first three phases of the operation in mid- to late September liberated 176 square kilometres of territory.

Ukraine's President Volodymyr Zelenskyy put the figure at between 125 and 140 square kilometres as of 3 October, adding that Russian losses had risen sharply over the preceding two to three months.

Ukrainian servicemen run along a street in Druzhkivka; photo provided by the press service of Ukraine's 93rd Separate Mechanised Brigade Iryna Rybakova/Ukrainian 93rd Mechanized brigade ISW suggested the operation may have been more successful than Kyiv’s official figures reflect.

The defeat of the northern pincer forced Russia to abandon its plans to advance on Sloviansk from the north-east and deprived it of positions intended to threaten northern approaches to the fortress belt.

Ukrainian servicemen watch a first-person-view (FPV) drone in Druzhkivka on 12 September 2026.

Ukraine’s retained control over the Lyman area also preserved key supply routes. Russian units on other parts of the front may have been redeployed to reinforce the northern sector.

Russia’s south-western advance from the Pokrovsk–Dobropillia area — the surviving arm of the original encirclement — now faces far more ambitious objectives on its own.

ISW regards the collapse of the northern pincer as an operational failure, as Russia has not just lost ground around Lyman but also a key component of the campaign plan for the fortress belt.

Russian forces retain limited gains around Kostyantynivka and east of Sloviansk but have struggled to sustain the pace of advance in both areas.

Settlements liberated in Operation ISW argued that their reliance on infantry infiltration, drones and bombardment can produce gradual attrition but cannot generate the fast mechanised manoeuvres required to collapse Ukraine’s defences at the scale Moscow needs.

The situation remains fluid, the institute added, and Russian forces will probably adapt over time, but for now, Ukraine appears to have halted the advance.

A further Russian mobilisation and technological adaptation could alter the balance, although neither would necessarily enable a breakthrough.

Putin’s September figures challenged ISW also challenged claims, widely circulated in pro-government Russian media, that Russian forces occupied further 1,301 square kilometres of Ukrainian territory in September alone, roughly two and a half times the figure reported in previous months.

Based on geolocated photo and video footage, satellite imagery and visually confirmed data, the institute calculated that Russian assault units had in reality been pushed out of at least 80 square kilometres in September.

Russia's net retreat in September rose to 175.18 square kilometres, including areas it temporarily penetrated but did not hold.

Putin told the Valdai Club last week that Russia now occupies 89% of Donetsk region. ISW puts the figure of Russian-occupied territory in the Ukrainian region at no more than 81%.

A local resident pushes her belongings in a cart along the streets of Druzhkivka in Ukraine's Donetsk region on 12 September 2026.

The institute assessed that Putin’s claims of Russian breakthroughs in September were “so far removed from reality that they resemble hallucinations.”It could not determine whether Putin knows the figures he cites are false or has come to believe the fabricated frontline data he receives, a product of what ISW describes as a deeply embedded culture of dishonesty in the Russian military command.