US makes exceptions for North Korea travel ban

The State Department's ban is set to go into effect on Sept. 1.

The ban will go into effect on Sept. 1 and will make it a felony to use a U.S. passport to travel to North Korea.

Waivers will be valid for one round trip to the country. The State Department estimates 100 people will apply for the waivers.

The department posted its official notice of the policy in the Federal Register today, which means that there are now 21 days for the public to comment on it and 30 days until it may be implemented.

North Korea is known to be holding at least three other Americans, two of whom were working at Pyongyang University of Science and Technology when they were detained this spring.

There are a few dozen U.S. citizens who work at the institution, which is the country's only private university and whose staff includes 60 to 80 foreigners throughout the academic year.

It's unclear if those Americans will be permitted to continue working in North Korea. Some are dual nationals who could travel using their other passports. The State Department specified in its notice that "use of a U.S. passport" will be invalid.

Each year, 800 to 1,250 Americans visit North Korea, although that number is expected to decline sharply this year, after Warmbier's death and the travel ban.

The ban is officially known as a geographic travel restriction, which gives the secretary of state the ability to bar travel to an area or a country if "the country is at war with the United States, armed hostilities are in progress in the country or area or there is imminent danger to the public health or physical safety of U.S. travelers in the country or area," according to the notice filed by the State Department.

ABC News' Ben Gittleson contributed to this report.