KHARKIV, Ukraine (AP) — Ukrainian troops are piling pressure on retreating Russian forces, pressing a counteroffensive that has produced major gains and a stunning blow to Moscow’s military prestige. As the advance continued Tuesday, Ukraine’s border guard services said the army took control of Vovchansk — a town just 3 kilometers (2 miles) from Russia seized on the first day of the war. Russia acknowledged that it has withdrawn troops from areas in the northeastern region of Kharkiv in recent days. It was not yet clear if the Ukrainian blitz could signal a turning point in the nearly seven-month war. But the country’s officials were buoyant and released footage showing their forces burning Russian flags.