South Korea's military said Thursday that a North Korean soldier had crossed the border between the rivals to defect. South Korea's Joint Chief of Staff said military officials were investigating the North Korean solider, who defected across the central-east portion of the military demarcation line, which is inside the 4-kilometer-wide (2.5-mile-wide) Demilitarized Zone that separates the countries. The military provided no other details. The Koreas have shared the world's most heavily fortified border since the end of the 1950-53 Korean War. The conflict ended with an armistice, not a peace treaty, leaving the Korean Peninsula in a technical state of war. Despite the heavy military presence at the border, North Korean soldiers occasionally find room to sneak into the South. Another North Korean solider defected in June last year after crossing the military demarcation line. More than 29,000 North Koreans have defected to capitalist South Korea since the end of the Korean War, according to Seoul's government.