SEOUL, South Korea >> A group of American and Canadian humanitarian workers who were traveling in North Korea recently had to make a tough decision: leave the country immediately and hope to return to their lifesaving work in the future, or stay in the North and face possible problems trying to go home later.

This time, however, the uncertainty of their situation was not because of the North Korean government, but rather because of the Trump administration’s intention to bar Americans from traveling to the already isolated country. Under the order, announced in July, Americans must leave the North by Sept. 1.

“I didn’t want any of the staff or any of the colleagues to potentially face issues when they were getting out,” said Kim Taehoon, founder of DoDaum, a humanitarian group based in the United States that has organized an HIV-diagnosis and treatment program in North Korea for the past several years. “Because of the uncertainty of the travel ban, we don’t know if we will be able to do on-the-ground work anymore,” Kim said.

Washington announced the ban in response to the death of Otto F. Warmbier, 22, an American college student who had been serving a 15-year sentence of hard labor in North Korea after being convicted of trying to steal a political poster. Warmbier died in June shortly after the North released him in a coma. The travel restrictions also reflected the United States’ growing impatience with North Korea over its missile tests and pursuit of nuclear weapons.

By imposing the travel restriction, Washington hopes to discourage people from visiting North Korea, whose brutal government has detained American visitors for offenses like leaving a Bible behind in a hotel room. But at the same time, the sweeping ban threatens the work of hundreds of humanitarian workers in the North — Americans and those who collaborate with them — and the lives of North Koreans who badly need help.

“One way or another, this program must go on. Otherwise, lives are lost,” said Stephen W. Linton, an American who oversees the Eugene Bell Foundation, a nonprofit group that has treated 250,000 tuberculosis patients in North Korea since 1997, including those with multidrug-resistant strains of the disease that are costlier to treat and more difficult to cure.

Every six months, Linton leads a delegation of about 12 volunteer health care specialists, half of them American, on a three-week trip to North Korea. During the visits, which take place in May and November, they examine new patients and discharge from care those who have completed an 18-month treatment program. The treatment must follow a strict schedule to be effective, hence the delegation’s fixed schedule for trips.

Now, Linton is fretting over whether his team can visit in November.

Under the ban, U.S. passports are invalid for travel “to, through and in North Korea,” according to the State Department. The department says that “in extremely limited circumstances,” it can consider a special validation visa for humanitarian workers, Red Cross officials, journalists and others traveling for “the national interest.” They must apply for it each time they want to visit North Korea.

Before the ban, an estimated 1,000 Americans had been traveling to North Korea on organized tours each year. Hundreds of humanitarian workers operated there at any given time, with most allowed to stay for only a limited duration. As the travel restriction loomed, major humanitarian groups, like World Vision or the American Friends Service Committee, said they had no resident or visiting workers in the North.

It is unknown how many Americans are still in the North in ignorance or defiance of the ban. Also unclear is how effectively the United States will enforce it. “U.S. citizens are not required to register their presence with the U.S. government,” said William Cocks, a spokesman for the State Department’s Bureau of Consular Affairs.

North Korea has called the ban “childish” and has said it will keep its doors “wide open to any U.S. citizen who would like to visit our country out of good will.”

Kim, the DoDaum founder, said a 15-member delegation from his group had been cleared by the North Korean authorities to visit in mid-September to deliver HIV medication and help treat patients, but the trip had to be canceled. Kim is a Canadian citizen, but key members of the delegation are Americans affected by the ban.

As a way around the restriction, DoDaum is joining with the Pyongyang University of Science and Technology to create an online medical education program so that volunteer professors can offer lessons remotely, Kim said.

The university, a private school in the North Korean capital that is financed by evangelical Christians, has relied on dozens of volunteer teachers, mostly Korean-Americans. Now, it must find non-American replacements if no exemptions are offered.

“I think this travel ban is being seen by North Korean officials as an explicitly inflammatory measure,” Kim said. “When we informed them of the need to pull out, there was a sense of understanding but at the same time, there was a sense of disappointment on both sides really.”

Supporters of the restriction say it will limit the chances of North Korea taking American hostages as diplomatic bargaining chips. In the past, it often released American detainees only after visits by prominent Americans like former President Bill Clinton.

It is still holding three U.S. citizens, two who were volunteers at the Pyongyang university, on vague charges of committing “hostile acts.”

The ban, by squeezing the flow of tourist cash, also helps international efforts to undermine North Korea’s ability to finance its nuclear and missile programs.

But critics of the ban say it will further restrict people-to-people interactions between the United States and North Korea. Among the hardest hit will be Korean-Americans who have been visiting North Korea to trace their family roots or for reunions with long-lost relatives.

“Restricting humanitarian access puts lives in immediate jeopardy and increases the likelihood of humanitarian disaster,” said Daniel Jasper, advocacy coordinator for the American Friends Service Committee, a Quaker organization that has provided humanitarian relief in North Korea for decades. “Our long history in the region leads us to believe that the travel restrictions will greatly reduce the likelihood for peaceful relations on the Korean Peninsula.”

American humanitarian workers said that the travel ban endangered the trust with the North Koreans that they had spent years building. To the North Korean authorities, who are hard-wired to consider Washington a mortal enemy, the fact that these American workers volunteered to visit despite their government’s warnings had been part of their credibility.

“Getting permission from the government to go puts an X mark on your back because the North Koreans will never believe that you are there just for humanitarian purposes if the government gave you permission to go,” Linton said. “In fact, this travel ban, the way it’s set up, puts NGOs in much greater danger by requiring official government permission to travel to North Korea.”

“There is no one I know in North Korea who would believe that there isn’t some connection between the NGO and the government that made that permission possible,” he added.

For Linton, helping Koreans has been a family mission for more than a century.

His grandfather’s father-in-law, Eugene Bell, arrived in Korea in 1895 as an American missionary to engage in medical and evangelical activities. Linton’s grandfather, William Linton, also a missionary, served in Korea for half a century. In 1995, Linton established the Eugene Bell Foundation to help tuberculosis patients in North Korea.

The members of Linton’s North Korean mission show that same dedication, including an 83-year-old Catholic priest who has been visiting the North despite a heart condition.

They are determined to return, even if that means signing a waiver forsaking their right to consular service — a move they hope will make it easier for them to receive permission from the U.S. government to travel to the North.

“We are not going to hold the U.S. government responsible for trying to get us out if we get into trouble,” Linton said. “We are doing this as mature adults who have made a decision that this program is worth the risks involved.”