On Tuesday, his lawyers said they doubted the truth of the allegations, and questioned how the connections would not have been uncovered during the months of vetting that he endured before being granted a visa to enter the United States.

“I find it really hard to believe that something that obvious slipped by the Department of State for a year,” said Kerry Doyle, one of the lawyers.

Mr. Dehghani had previously spent two years studying at the University of Massachusetts and at least a semester at Northeastern University. He had returned to Iran in 2018 to spend time with his family, his lawyers said.

In interviews with 10 of the Iranian students who have been removed since August, many said that their visas had taken months to be processed, and that they had spent their entire savings, or taken out loans, to pay for plane tickets, entrance exams and university applications.

Even after crossing those hurdles, many said, they had been humiliated during the process of being vetted at airports, by being walked around by armed guards. One of the students said he was forced to wear handcuffs and leg cuffs.

Some of the students said they were brought to small, cell-like rooms with threadbare furniture and mattresses, and were not told how long they would have to stay there. They were not allowed to speak to family members or lawyers until they had arrived in other countries for layovers en route to Iran.

One young man named Amin, who asked to be identified by his first name to avoid jeopardizing his chances of being admitted to study in another country, said he was on his way to start a Ph.D. program at the University of Florida on Jan. 1 when he was pulled aside by an officer at the airport in Atlanta. The officer took him to a room for questioning while his suitcase and cellphone were searched by other officers in a separate room.