The ban that began under President Donald Trump is now extended for one year until Aug. 31, 2022, the State Department announced. It was initially implemented in 2017 by former Secretary of State Rex Tillerson following the death of American university student Otto Warmbier, who sustained intense injuries under North Korean custody and ended up in a coma.

“The Department of State has determined there continues to be serious risk to U.S. citizens and nationals of arrest and long-term detention constituting imminent danger to their physical safety,” the department said in a Federal Register notice to be published Thursday.

“Accordingly, all U.S. passports shall remain invalid for travel to, in, or through the DPRK unless specially validated for such travel under the authority of the secretary of state,” the notice added.

Since Warmbier’s death, the ban has been extended each year. In 2016, he was a part of a tour group visiting North Korea and as he was departing the country, he was arrested after being accused of stealing a propaganda poster. After his conviction, he was sentenced to 15 years in a North Korean prison.

The extension of the passport ban comes days after the U.N.’s International Atomic Energy Agency (IAEA) reported North Korea appears to be restarting its main nuclear reactor to produce plutonium, which can be used to develop nuclear weapons, the Associated Press reported.

“(North Korea’s) nuclear activities continue to be a cause for serious concern,” the agency said.

For more reporting from the Associated Press, see below.

Humanitarian groups have expressed concern about the impact the initial ban and its extensions have had on providing relief to isolated North Korea, which is one of the world’s neediest countries.

The ban makes it illegal to use a U.S. passport for travel to, from or through North Korea unless the document has been specially validated. Such validations are granted by the State Department only in the case of compelling national interest.

In June 2017, North Korean authorities reported to U.S. officials that Warmbier had suffered extensive injuries while in custody, and Trump’s administration sent a delegation to repatriate him.

Comatose, Warmbier died in a Cincinnati hospital six days after his return to the U.S. Shortly thereafter, Tillerson imposed the ban on the use of U.S. passports for travel to North Korea.