North Korea fully reopened its border Tuesday to South Koreans commuting to jobs at factories in a northern economic zone after four days of restrictions, South Korean officials said. The crossing was closed twice in a week, stranding hundreds of South Koreans who work in Kaesong and keeping new deliveries of raw materials from factories in the industrial complex for days. After partially opening the border Monday, the North Korean military relayed a letter Tuesday saying it would fully reopen the crossing to Kaesong workers, Unification Ministry spokeswoman Lee Jong-joo said in Seoul. North Korea has provided no explanation for the closures, which have unnerved business owners who rely on South Korean managers and raw materials for factories that employ some 38,000 North Korean workers just across the border. But Pyongyang has been critical of Seoul's decision to hold 12 days of joint military exercises with the US at a time of heightened tension on the peninsula.