EAST LANSING, Mich. (AP) — U.S. authorities declined to admit an Iranian graduate student after he landed at an airport to start classes at Michigan State University, an attorney said.

Alireza Esfidajani, 27, was stopped Sunday at Detroit Metropolitan Airport and interviewed by agents. He was held at a jail in Monroe County and returned to Iran on Monday.

“They deemed him being inadmissible but they never said under what grounds,” attorney Ghazal Nicole Mehrani told The Detroit News. “They just told him it’s better to withdraw his admission. That’s what he did.”

U.S. Customs and Border Protection didn’t offer a specific reason to the newspaper about why Esfidajani was denied entry.

“Every applicant for admission is subject to inspection upon arrival into the United States,” the agency said. “The issuance of a visa or participation in the visa waiver program does not guarantee entry to the United States.”

Esfidajani was supposed to start classes soon, MSU spokeswoman Emily Gerkin Guerrant said.

“Global leadership can only be maintained if talented people from across the globe are encouraged to come here to study and work,” she said.