DNIPROPETROVSK, Ukraine — When the Donbas Battalion stormed Russian separatist-held Ilovaisk on Aug. 18 and raised the Ukrainian flag without a single casualty, the Ukrainian media quickly reported a victory for the country’s anti-terrorism operation against Kremlin-backed insurgents.

The Interior Ministry announced that four volunteer battalions along with the regular army were clearing Ilovaisk, a city of 17,000 residents southeast of Donetsk, of Russian-backed forces, and promised that more back-up from the National Guard was on its way.