Ukrainian army snipers near Bakhmut.AP Photo/Libkos Russian defenses are "likely brittle" amid the ongoing Ukrainian counteroffensive, the ISW said. The think tank noted that Russian forces likely lack the reserves to rotate frontline units. If Ukraine breaks through, Russia would have to rely on its "already degraded forces." Russian defenses in Ukraine are "likely brittle" amid the ongoing Ukrainian counteroffensive, according to a think tank.In an update on the Russia-Ukraine conflict, the Institute for the Study of War said its analysis was supported by the recent dismissal of top Russian general Major General Ivan Popov, who said he was removed from his position after raising questions about mass Russian casualties from Ukrainian artillery and a lack of support for Russian forces.Popov reportedly claimed that he had appealed to his superiors to rotate troops and relieve those who had fought on the frontlines for a long time.The ISW said Popov's comments reinforced their previous assessments and indicated that rotations and reinforcements are needed to sustain Russian defenses in western Zaporizhzhia.