The United States government has decided to bar Americans from visiting North Korea, the first time in years that the State Department has moved to block travel to another country.

The restriction comes amid rising tensions between the United States and North Korea, which has been testing intercontinental ballistic missiles and threatened to attack the United States with nuclear weapons. The ban also follows the death in June of Otto F. Warmbier, the University of Virginia student who was convicted of trying to steal a political propaganda poster from his hotel in Pyongyang. This is the first time in more than a decade that the State Department has taken such strong measures. It was in the early 1990s during Saddam Hussein’s regime that travel to Iraq was restricted.

“Due to mounting concerns over the serious risk of arrest and long-term detention, the department will soon impose a travel restriction on all U.S. nationals’ use of a passport to travel in, through or to North Korea,” Susan A. Thornton, the acting assistant secretary of the Bureau of East Asian and Pacific Affairs, said in a statement on July 25. “We seek to prevent the future detentions of U.S. citizens by the North Korean regime to avoid another tragedy like that which Otto Warmbier and his family endured.”

Heather Nauert, a State Department spokeswoman, said late last month during a news briefing that the travel ban would go into effect 30 days after it was listed as a legal notice in the Federal Register.

“I saw in one major newspaper today where people were talking about, oh, there are neat experiences in North Korea, which makes it sound like it’s a fantastic place to go,” Ms. Nauert said. “Let me use this as an opportunity to remind people: It is not safe for Americans to go to North Korea. Let me remind you, we still have Americans who are being detained in North Korea. We don’t want to see any more people go to North Korea and be detained, and that is why we put that travel ban in place.”

There may be exceptions, though. For example, Ms. Nauert said journalists could apply to enter the country at the discretion of the State Department.

For years, Americans have been free to travel to other countries, even places that are dangerous and war torn, including Afghanistan. Travel to Cuba, while at times limited to certain individuals or to those with special licenses, has been allowed since the late 1970s. Still, the North Korea ban is hardly the first time the United States has restricted travel to other countries.

“In 1952, during the Cold War, all American passports were amended with a stamp indicating they weren’t valid for travel to China, the Soviet Union and other Warsaw Pact nations without a State Department exemption,” The Associated Press reported. Subsequent bans where passports from the United States were invalid for travel have included Iran, Lebanon and Libya.

The State Department regularly issues strongly worded alerts and warnings to citizens about security threats throughout the world, posting them on its website and social media accounts, and making them available through email alerts. For instance, the department “warns U.S. citizens against all travel to Iraq” and that “U.S. citizens in Iraq are at high risk for kidnapping and terrorist violence.” Even so, Americans can still travel there.

The same has been true of North Korea. In May, the department warned Americans about the “serious risk of arrest and long-term detention” in North Korea, yet it had not barred travel there.

“This news has been expected but nevertheless is something of a shock, and we’re sorry for anyone who had planned a trip or who had hoped to visit and who now will not be permitted to do so,” Koryo Tours, one of several companies that offer tours to North Korea, said in a statement in anticipation of the ban. The company, which is based in Beijing, said that it will continue taking American citizens to other far-flung destinations, including Tajikistan, Turkmenistan, Mongolia and the Russian Far East.

A handful of operators have lead Americans on tours to North Korea, including Lupine Travel, which is based in Britain; Uri Tours, based in New Jersey; and Young Pioneer Tours, based in China.

Young Pioneer, the company that took Mr. Warmbier to North Korea on a five-day tour, advertised “budget travel to destinations your mother would rather you stayed away from.” In January 2016, Mr. Warmbier was about to board a plane home when he was detained at the Pyongyang airport. He was convicted weeks later of trying to steal a propaganda poster and sentenced to 15 years of prison and hard labor. He was returned to the United States this year in a coma, and died on June 19. He was 22.

Young Pioneer Tours said that Mr. Warmbier’s death had led it to reconsider its position on accepting American tourists, and that it would no longer organize tours for American citizens to North Korea. “There had not been any previous detainment in North Korea that has ended with such tragic finality and we have been struggling to process the result,” the company said in a statement. “Now, the assessment of risk for Americans visiting North Korea has become too high.”

The State Department does not track the number of American travelers to North Korea, but tour operators have estimated that it is about a few hundred each year. The majority of tourists are Chinese.

Han Chol-Su, a vice director of the Wonsan Zone Development Corporation, which is promoting tourism on the east coast of North Korea, told Agence France-Presse in Pyongyang that the loss of business as a result of the United States ban would not hurt North Korea. “If the U.S. government says Americans cannot come to this country, we don’t care a bit,” he said.