Dozens of American faculty members at North Korea university face diplomatic limbo The university says a new U.S. restriction may force it to suspend operations.

 -- As the last foreign faculty members remaining at North Korea’s only private university leave the country this week, it remained unclear whether they will be able to return this fall -- thanks to the Trump administration’s plans to bar Americans from traveling to the reclusive country.

The Pyongyang University of Science and Technology, whose faculty includes 60 to 80 foreigners throughout the academic year -- half of whom are Americans -- would likely have to suspend operations if it did not receive an exemption from the forthcoming restriction, according to Colin McCulloch, the institution’s director of external relations.

"If we didn't get an exception, we would basically have to stop our work,” McCulloch, who has taught business, economics and English at the school since it first opened to North Korean students in 2010, told ABC News. "That’s how serious it would be. Because we would not be able to provide enough personnel.”

The U.S. State Department said Friday it would soon bar Americans from using their passports to travel to, through or in North Korea, and would issue waivers for citizens only for “certain limited humanitarian or other purposes.” The move comes amid heightened tensions between Washington and Pyongyang and following the death last month of an American college student days after North Korea released him from detention.

North Korea is known to be holding at least three Americans, two of whom had worked with PUST and were detained this spring.

Tony Kim, who also goes by his Korean name, Kim Sang-duk, taught accounting at the university before he was detained at an airport in April and charged with unspecified hostile criminal acts, and Kim Hak-song was held in May after spending several weeks doing “agricultural development work with PUST’s experimental farm,” the university said at the time. He was also charged with unspecified “hostile acts.”

The university has said it understood the arrests to not be linked to the school’s work.

When PUST is fully staffed during the academic year, around 50 American faculty members and their family members live on the Pyongyang campus, out of over 100 foreigners total, McCulloch, the spokesman, said. They make up a significant percentage of the Americans who reside in North Korea.

McCulloch said he hopes members of the school’s leadership, many of whom are Americans, will be able to obtain an exemption for the U.S. faculty ahead of the fall semester, due to begin at the start of September. He said they had dealt similarly with sanctions in the past.

The State Department said the restriction would apply 30 days after it officially filed notice of it sometime this week. A senior official said anyone could apply for a waiver, but the department has not responded to questions about whether PUST faculty members would be eligible for them.

It is unclear if Americans with dual citizenship will be permitted to use their other passports to travel to North Korea, although McCulloch said only a few American faculty members were dual nationals.

Wesley Brewer, an American who has taught computer science at PUST since 2010 and now serves as the institution’s vice president of research, said that the arrests shook the university community and affected him deeply. He told ABC News now looked like a good time for him to take a long-planned sabbatical.

“Being an American there, you feel like you’re standing right in between the two countries and maybe preventing some kind of moving forward, in terms of diplomatically,” Brewer said.

Brewer splits his time between Seoul and Pyongyang and spoke from Jackson, Mississippi, where he was visiting a church that supports his work. “I just felt like with the heightened tensions, it seemed it would be wiser to step back and let things settle down before re-engaging,” he said.

Most of PUST’s faculty members, who do not receive salaries, are devout Christians who see the school as a way to engage in charity work and build bridges between North Korea and the outside world, according to several faculty members. Most come from the United States, Canada and Europe, and a majority of the Americans who have taught there are Christians who are ethnically Korean and have been supported by churches in the United States, they said.

Directly preaching to or attempting to proselytize North Koreans is prohibited, although the foreigners are allowed to observe their faith in private, they said.

Donations from churches and individuals in South Korea and the Korean diaspora fund the school’s approximately $2 million annual operating budget, according to McCulloch.

In addition to English classes, PUST offers its students -- 650 during the last semester -- courses in business, engineering, medicine, dentistry, life sciences and agriculture, among other subjects. Foreigners provide almost all instruction, which must gain prior approval from North Korean authorities, McCulloch said.

Richard Roberts, a Nobel laureate who visited the university and two others in North Korea in spring 2016, said the PUST instructors he met sounded as if they had traveled extensively within the country. He said he was surprised by how much the students knew of their fields despite their lack of direct access to the internet.

“The students, I thought, were actually quite good,” Roberts told ABC News. “They were fairly well educated. They knew much more about modern science and what was going on in the rest of the world than I had first anticipated.”

McCulloch said he was not aware of the arrests affecting faculty recruitment but that general “geopolitical noise” had already made an impact.

That tension had not reached the campus yet this spring, though, at least not in faculty-student discussions, according to a Dominik Naeher, a German Ph.D. candidate who taught econometrics at PUST for several months this year. “With the students, there was no effect whatsoever,” Naeher, who lives in Frankfurt, told ABC News. “We didn’t talk about it.”

“But of course,” Naeher added, “among us foreigners, we were talking about it -- about the news -- and hoping that war wouldn't break out.”

Naeher lived in Pyongyang with his wife and 1-year-old son. Despite the worries, he said he would return as soon as possible.

ABC News’s Conor Finnegan contributed reporting from Washington, D.C.