An American scholar and former diplomat who has been a vocal critic of Egypt’s authoritarian government said Saturday that she had been turned away at Cairo’s international airport — the latest instance of an academic running afoul of the administration of President Abdel Fattah al-Sissi.

Michele Dunne, a senior associate at the Carnegie Endowment for International Peace, flew to Cairo at the invitation of the Egyptian Council for Foreign Affairs and was to have been a panelist at a conference organized by the group.

“Authorities denied me entry at the airport, deporting me after holding me for about six hours,” Dunne said in an e-mail sent during a stopover on her way back to Washington. “I asked for a reason, but they refused to give me one.”

Dunne said she has visited Egypt several times each year for more than a decade without incident. She has written reports critical of Egypt’s curtailment of freedom of expression and the jailing and intimidation of government critics.

A spokesman for Egypt’s Foreign Ministry did not respond to a request for comment.

Sissi — first as defense minister, then as president — has overseen a wide-ranging campaign against dissent during the past 18 months. The principal target has been the Muslim Brotherhood of deposed Islamist President Mohamed Morsi, but secular figures including filmmakers, journalists, activists and professors have also been caught up in the crackdown.

On Saturday, the Associated Press reported that Egypt’s top prosecutor has referred 439 people to military tribunals for acts of violence including the killing of three policemen last year. Security officials, speaking on the condition of anonymity because they were not authorized to speak to the news media, said the cases involve last year’s wave of violence in response to a bloody police dispersal of an Islamist sit-in.

Since Morsi was deposed in July 2013, more than 16,000 of his followers have been jailed and hundreds have been killed in street clashes with police. Morsi is on trial, charged with a variety of capital offenses, and the Brotherhood, once Egypt’s largest political movement, has been branded a terrorist organization.

Egypt has barred foreign critics in the past. Four months ago, the executive director of Human Rights Watch, Kenneth Roth, and regional director Sarah Leah Whitson were denied entry before the release of a report detailing what the group called possible crimes against humanity by the Egyptian government.

Although the targeting of a foreign academic is unusual, several prominent Egyptian scholars have found themselves under threat of prosecution or had their travel restricted.

Political scientist and former member of parliament Amr Hamzawy was forbidden for months from leaving the country after a tweet deemed insulting to Egypt’s judiciary. Emad Shahin, who has taught at Harvard and served as editor in chief of the Oxford Encyclopedia of Islam and Politics, left Egypt nearly a year ago after learning that prosecutors had filed espionage charges against him.

— Los Angeles Times