The U.S. government will soon prohibit its citizens from traveling to North Korea, the State Department announced Friday, citing “mounting concerns over the serious risk of arrest and long-term detention.” While the U.S. previously discouraged Americans from making trips to North Korea, the new policy legally restricts the “use of a passport to travel in, through, or to North Korea,” said State Department spokeswoman Heather Nauert. According to Nauert, the ban will be published in the Federal Register on July 27 and will become official after 30 days. She added that those who wish to travel for “certain limited humanitarian or other purposes” could apply for a special passport.

The decision comes more than a month after Otto Warmbier, the University of Virginia student who was sentenced to 15 years of hard labor for allegedly stealing a propaganda sign from his hotel in North Korea, died after returning to his Cincinnati home. Warmbier arrived in North Korea in December 2015 as part of a tour group, but was arrested as he was leaving the country. North Korean officials claim that he contracted botulism shortly after his trial and was given a sleeping pill, which led to a coma. Upon his release, Warmbier was unable to see, speak, or respond to verbal commands, his family said. He was soon taken to the University of Cincinnati Medical Center, where doctors claimed that he suffered from cardiac arrest, not botulism.

In the wake of Warmbier’s death on June 19, his parents said he had been “brutalized and terrorized” while in prison. They argued that their son had become “fodder” for the North Korean regime, which has detained at least three other U.S. citizens on charges such as spying and “hostile acts.” The White House has previously accused North Korea of detaining U.S. citizens to use them as leverage in negotiations surrounding its nuclear program. Freeing Warmbier was reportedly a “big priority” for President Trump, whom Warmbier’s father has since credited for his son’s release. “Otto’s fate deepens my administration’s determination to prevent such tragedies from befalling innocent people at the hands of regimes that do not respect the rule of law or basic human decency,” Trump said in June.

Following Warmbier’s death, the tour group that organized his trip—Young Pioneer Tours—announced they would no longer take U.S. citizens to North Korea, arguing that “the assessment of risk for Americans visiting North Korea has become too high.” At the same time, two other tour groups that work with Americans—Beijing-based Koryo Tours and New York- and Shanghai-based Uri Tours—said they were reviewing their policies. Koryo Tours has since told the BBC that they will continue to work with U.S. citizens until the ban goes into effect. “If their country allows them to go, we will take them,” said Simon Cockerell, the group’s general manager. He added that the ban is “unfortunate for the industry, but also for North Koreans who want to know what Americans are really like.”

In addition to the State Department ban, Congress is considering a bill that would outlaw the majority of U.S. travel to North Korea for five years. Those who wish to make the trip for non-tourism-related purposes would be required to obtain a license from the Treasury Department. Part of the goal, according to lawmakers, is to cut off tourism funds to North Korea. But, as many experts have pointed out, the vast majority of tourists who visit North Korea come from China, the nation’s only major ally. Koryo Tours, for instance, estimates that it only takes around 400 Americans to North Korea each year—suggesting that a travel ban, while politically significant, could have little economic influence.