Seoul: North Korean troops have crossed the heavily fortified inter-Korean border on more than 20 occasions last month, military officials said Wednesday. North Korean soldiers crossed the Military Demarcation Line (MDL) on the eastern front for the first time in mid-August, and they have since repeatedly engaged in border crossings, according to military officials. According to Yonhap News Agency, the number of MDL crossings by North Korean troops in August surpassed a total of 17 reported cases for the whole of 2025. "Intrusions were detected as North Korean troops have conducted (border fortification) tasks in areas that are yet to be completed," a Joint Chiefs of Staff (JCS) official said. "The intrusion does not seem to constitute changes in North Korean troops' activities or indicate any unusual activity," the official added. Since 2024, North Korea has bolstered border fortification work by installing barbed-wire fences and landmines along the border. The move followed North Korean leader Kim Jong-un 's declaration of inter-Korean relations as those between "two hostile states" in late 2023. In response to the border crossing, the South Korean military said it fired warning shots. Under rules of engagement, the military is obliged to issue warning broadcasts when North Korean troops approach the MDL, and fire warning shots when they cross the border. The JCS said it is reviewing ways to step up surveillance along the border, including installing monitoring devices inside the Demilitarized Zone (DMZ) northward.