The city of Lutsk, home to airfields used by the Ukrainian army, was the hardest hit, according to Ukrainian President Volodymyr Zelenskyy. It lies in western Ukraine near the border with Poland, a region that is a crucial hub for receiving foreign military aid.

The attack comes at a time of increased uncertainty over the supply of crucial American weapons and as U.S.-led peace efforts have stalled. Zelenskyy said that the Kremlin was “making a point” with it.