The commander in chief of the Ukrainian military, Col. Gen. Oleksandr Syrskyi, said Thursday that the Kursk offensive has been effective and the “strategy is working” to block Russian forces from taking more territory in eastern Ukraine.

Syrskyi told CNN’s Christiane Amanpour that the Kursk operation “reduced the threat of an enemy offensive” and prevented a Russian attack, saying Moscow had amassed tens of thousands of troops in the region, including experienced airborne ones.

He also said that Ukrainian forces have stalled the Russian advance in eastern Ukraine, including around the strategic railroad town of Pokrovsk.

“Over the last six days the enemy hasn’t advanced a single meter in the Pokrovsk direction. In other words, our strategy is working,” he said. “We’ve taken away their ability to maneuver and to deploy their reinforcement forces from other directions … and this weakening has definitely been felt in other areas.”

Syrskyi’s comments come as Ukrainian forces face a massive Russian attack in Ukraine’s eastern Donetsk region, with troops closing in on not only Pokrovsk but also the cities of Chasiv Yar and Toretsk, both of which could help Russia advance further if captured.

Ukraine made a surprise incursion into Russia’s Kursk region on Aug. 6, a move that caught Moscow off guard and was initially hailed as a brilliant counteroffensive that demonstrated the Kremlin had weak borders.

But nearly a month since the incursion, Ukraine has not achieved one of its main objectives — diverting a sufficient number of Russian troops from the front lines to Kursk to ease up pressure there — leading to criticism of whether the gamble worked....