Ukrainian forces are fleeing the strategic region of Kursk after Russia took the city of Sudzha in a lightning offensive. In August, Ukraine launched the first invasion of Russia since World War II, rapidly seizing roughly 386 square miles centered on the city of Sudzha.

Russia said on Thursday there was no doubt that its troops would soon complete the task of clearing out Ukrainian forces from Russia's Kursk region where they have held a pocket of territory for more than seven months.

President Trump and President Vladimir V. Putin both claimed that Ukrainian forces were surrounded. Ukraine’s top military commander vowed to “hold the line.”