U.S. President Donald Trump speaks with reporters before boarding Air Force One at Morristown Municipal Airport in Morristown, N.J., Sunday, Aug. 18, 2019. AP

The United States on Monday extended a ban on American citizens traveling to North Korea for another year.

The State Department announced the extension in a notice, saying "there continues to be serious risk to United States nationals of arrest and long-term detention" in the North.

The notice is due to be published in the Federal Register on Tuesday.

The travel ban was imposed in September 2017 in the wake of the death of Otto Warmbier, an American college student who was detained in the North and died shortly after his return to the U.S. in a coma. Exceptions can be granted to journalists and for humanitarian reasons for a single trip.

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The measure was renewed once in 2018. It will now remain in place until Aug. 31, 2020, unless extended or revoked by the secretary of state.

The move follows a separate action by the U.S. this month, under which foreign nationals with a record of traveling to North Korea beginning in March 2011 must obtain a visa in order to enter the U.S.

Previously, countries that were part of the Visa Waiver Program, including South Korea, could use only the Electronic System for Travel Authorization to visit the U.S.

The U.S. and North Korea have sought to improve relations since U.S. President Donald Trump and North Korean leader Kim Jong-un met for their historic first summit in Singapore in June 2018.

But stalled negotiations on dismantling the North's nuclear weapons program have hampered the development of overall bilateral ties. (Yonhap)