The Ukrainian 3rd Army Corps used an intermediate-range strike campaign to target Russian logistics and fuel supplies during a counteroffensive named Operation Vivaldi. This effort thwarted a Russian plan to encircle Ukraine’s Fortress Belt from the north and south, rendering those specific maneuvers unfeasible. The Ukrainian military provided the first explicit confirmation of the operation on September 16, noting the objective was to block a Russian salient northwest of Lyman.

Ukrainian troops cleared 75 square kilometers of territory and retook the settlement of Serednie. OSINT analyst Clément Molin reported Russian losses of 240 square kilometers near Lyman. Russian forces launched 200 drones against Ukraine overnight. President Volodymyr Zelensky stated on September 15 that Ukraine is willing to engage in a mutual ceasefire on energy targets following a push from US President Donald Trump. The US Treasury Department added sanctions against VTB Bank on September 14 for involvement in Iranian sanctions evasion.