"There is mass hysteria among the Iranian-American community -- that's no exaggeration," said Saam Borhani, an attorney in Los Angeles.
He said clients were bombarding him with questions since Trump passed an executive order on Friday, suspending refugee arrivals and imposing tough controls on travellers from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen.
With more than one million Iranians living in the United States, the restrictions have already caused chaos for students, businessmen and families.
US State Department figures show Iran accounted for around a quarter of the 31,804 visas granted to citizens from the seven countries last year.
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Among thousands facing difficulties, an Iraqi family was barred in Cairo from taking their connecting flight to New York yesterday.
"I had sold my house, my car, my furniture. I resigned from work and so did my wife. I took my children out of school," Fuad Sharef, 51, told AFP.
An Iranian woman blocked from boarding at Tehran airport today said she had waited 14 years for her green card.
"Even during the hostage crisis at the US embassy (in 1980), the US government didn't issue such an order. They say the US is the cradle of liberty. I don't see freedom in that country," she said, asking not to be named.
The US embassy in Baghdad said on Facebook that dual nationals from the seven countries would be barred from entering the United States, excluding those with American passports.
He asked why the list excluded Afghanistan, Pakistan, Qatar and Saudi Arabia, which he described as the "biggest sponsors of terrorism".
Iran's Foreign Minister Mohammad Javad Zarif said today that Trump's move "will be recorded in history as a great gift to extremists and their supporters.