South Korea concluded with the U.N. Command that North Korean troops deliberately planted resin antipersonnel mines south of the Military Demarcation Line (the de facto border in the Demilitarized Zone), causing a Sept. 21 blast that wounded three South Korean soldiers, two seriously. Seoul has since cleared mines at the site in the first such operation inside the buffer zone, and officials say it plans to formally declare the North in violation of the 1950-53 war armistice, seek inter-Korean military talks and keep demanding an apology; Joint Chiefs chairman Jin Yong-sung called the incident a "provocation" and said further responses are under review. Pyongyang denies involvement, calling the findings a "farce", and Kim Yo-jong, sister of leader Kim Jong-un, has warned of "merciless" retaliation for any counteraction, raising the risk of escalation along one of the world's most heavily armed borders.