After Trump ordered a ban on travelers from Iran and six other Muslim countries, Iran retaliated by saying it would no longer issue visas for Americans, though the country's foreign minister suggested there might be exceptions.

Trump's travel ban is being challenged in U.S. courts, but uncertainty persists over travel in both directions.

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Wilderness Travel canceled April and May trips to Iran "with great regret," said spokeswoman Barbara Banks. "The increase of interest in travel to Iran had been a wonderful development; cultural exchange and understanding is the foundation for a peaceful world." The company had recently added three Iran itineraries, including one by train, after a successful 2016 trip.

Just two weeks ago, smarTours' co-CEO Greg Geronemus announced that several Iran trips sold out within 48 hours. "We believe Iran is the new Cuba," he said at the time. But last week, smarTours canceled a July trip to Iran because of visa uncertainties. SmarTours asked travelers to rebook on Iran departures later this year. "It will take a few months for this back and forth to resolve itself, but we are encouraged by the legal challenges and the political opposition within the United States to the travel ban," Geronemus said.

Iran says it gets 5 million tourists annually, mostly from neighboring countries like Iraq. Americans represent far less than 1 percent of Iran's tourists.

But it's striking that Americans want to visit Iran at all given the fraught history of U.S.-Iran relations, which include CIA support for a coup in Iran in 1953, the taking of 52 American hostages in Iran in 1979 and President George W. Bush calling Iran part of an "axis of evil."

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The U.S. Tour Operators Association listed Iran among 2017's top 10 emerging destinations along with Myanmar and Cuba. Iran itineraries often include luxury train travel, the Caspian Sea, bazaars, castles, museums, mosques and other religious sites ranging from Zoroastrian to Sufi.

Janet Moore, spokeswoman for tour company Distant Horizons, said interest in Iran is so strong that people are signing up "even though we are saying we can't guarantee that we can get visas." She believes Americans who do go will be welcomed because she is "not hearing anti-American rhetoric on the streets ... the (Iranians) are seeing all the messages of support which they can easily access and hear on TV and online."

Several companies, including Explore and Cox & King, are proceeding with trips because clients include travelers from around the world, but they're recommending U.S. passport holders rebook on other trips.

Intrepid Travel, which also serves travelers from around the world, ran 30 departures to Iran last year, has 40 scheduled this year and may add 20 more because of demand. "We have yet to confirm from our ground operators in Iran whether the visa ban is actually in place for U.S. travelers, but our team has been preparing for this potential result," Intrepid director Leigh Barnes said.

Some companies are in a wait-and-see mode, like Mountain Travel Sobek, which has been offering trips to Iran for four years.

Others are hoping for the best. Steve Kutay of Iran Luxury Travel thinks Iran will accept new visa requests and honor applications in the pipeline for his company's April and May trips. "I have never been in any country, and I have been to over 80, where Americans are more popular or welcome than in Iran," he said.

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Journeys International is also going forward with trips, said spokeswoman Sally Grimes-Chesak. The company started an Iran program in 2016 that proved so popular a women-only trip was added for 2017. That filled up so fast they added a second women's trip.

This is not the first time Iran has stopped authorizing visas, so the disruptions are not unprecedented. Depending on the tour company, Americans who can't get visas will get refunds or credit for other trips.

G Adventures has eight Americans booked on Iran departures in March and April but spokeswoman Kim McCabe said future visa approval "remains highly uncertain" despite increased interest.

"We see Iran as becoming an 'it' destination for trend-setting travelers, thanks in part to British Airways launching direct flights to Tehran late last year," she said. "Increased investment in tourism infrastructure is also making it easier to plan and sell travel to Iran, while European hospitality brands are making plans to open new hotels."

Americans contemplating travel to Iran should also consider the U.S. State Department warning, which notes that Iranian authorities have sometimes detained and imprisoned U.S. citizens, particularly Iranian-Americans.