A State Department notice released Monday says the ban will remain in place until Aug. 31, 2020. The ban was imposed in September 2017 by then-Secretary of State Rex Tillerson and renewed in 2018. Tillerson took the unusual measure following the death of an American student, Otto Warmbier, who had been detained in North Korea. The ban allows certain categories of American citizens such as aid workers or journalists to obtain a special validation passport good for one trip to North Korea. The move comes amid stalled diplomatic efforts to restart nuclear talks between North Korea and the US.