U.S. citizens have long been able to visit North Korea as tourists, but that will soon change. On Friday, the Trump administration announced that it was planning to bar U.S. tourists from traveling to North Korea next month.

The move coincides with increasing tension between the Trump administration and Pyongyang about North Korea’s nuclear weapons program. It also comes after Otto Warmbier, an American student, was detained while on a trip to North Korea and sentenced to 15 years of hard labor.

Warmbier later died, just six days after being released, in a comatose state, and flown to Ohio.

The decision to ban travel by U.S. citizens to a foreign country marks an unusual policy shift for the State Department, harking back to restrictions on travel not widely used since the Cold War era.