Iranian woman Nazanin Zinouri has been studying and working in the United States for the past seven years. She received her PhD in industrial engineering, specialising in optimisation and operations research and now works as a data scientist at Clemson University in South Carolina.

Last Monday the 29-year-old dropped her puppy off at her friend's house, parked her car in the long-term parking at Atlanta Airport and flew home to Iran for a short holiday.

Now, after US President Donald Trump issued an executive order temporarily banning people from seven Muslim-majority countries — including Iran — from entering the country, she has no idea when she will get back.

"About a day after I arrived here I started hearing rumours that there are going to be new immigration rules, not letting people from Muslim countries into the United States, but I thought 'it's all going to be rumours'," she said.

"Plus if something like that happens it's going to be for new visas, possibly for people trying to go there for the first time.

"They can't really … they're not going to stop someone who's been living there from going back to their homes?"

Last Thursday night in Tehran, Ms Nazanin sat glued to her TV, watching as Mr Trump signed the executive order. Despite having a valid visa, she began to worry about getting back home, so she decided to cut her long-awaited three-week holiday with her family short.

"That was really a terrifying moment, and I just decided to go ahead and find the earliest flight at any cost," she said.

On Friday Ms Nazanin boarded a flight that left Tehran at 8:10am, and she arrived in Dubai at 10:55am. She then got through security at Dubai and boarded her flight to Washington, which was due to depart about 3:00pm.

Nazanin Zinouri has been studying and working in the United States for the past seven years. ( Supplied: Nazanin Zinouri )

She was just settling into her seat when two transport security officials approached her and said they had been notified that she was traveling on an Iranian passport.

"There was lot of talking. A lot of going back and forth," she said.

"Obviously I was just terrified.

"I knew what was coming but I wasn't sure if it was actually happening, and after minutes and minutes of horror not knowing what's coming, finally, they removed me and they said I cannot go to the United States based on the new security rules."

After she was told she could not travel to Washington, Ms Nazanin was devastated.

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"There were a million thoughts going through my head," she said.

"Thinking of my life back there. Of my dog. I just thought, is somebody going to take care of him? What is going to happen to him?

Nazanin Zinouri with her dog Dexter, who she left with a friend in the United States. ( Supplied: Nazanin Zinouri )

"I thought about my job, my car that was at the airport. It was like a nightmare. It was like my life there was over."

Ms Nazanin fears she might never be able to go home again. She thought about how she left her house and all of her personal belongings. How is she going to get her stuff? What is she supposed to tell her family?

"It feels terrible to feel like other people are looking down on you," she said.

"I didn't go to the United States thinking that it's OK to treat people like this. I went to the land of democracy.

"I'm actually proud of being Iranian … did I have a criminal record, do I have any problems or do you even care to look at my background?

"Or is it just that one word in my passport that says 'country of citizenship: Iran'."