Egyptian authorities are increasingly harassing foreign academics with restrictions, bans on entering the country and deportations. Particularly targeted are those researching anything related to Egypt's "revolution" or social issues like organized labor — the Ph.D. topic of an Italian student recently killed under mysterious circumstances.

The case of Giulio Regeni has only deepened worries among academics that they are being caught up in a crackdown that Egypt's government has waged the past two years against dissent. Regeni disappeared on the fifth anniversary of Egypt's Jan. 25, 2011 uprising, and his body turned up days later with marks of torture.

Egypt's Interior Ministry has denied security forces were involved in his death and said he was never detained by police.

Academics say the past years of harassment show how sensitive research work is in the eyes of authorities — especially amid a public atmosphere where foreigners are depicted in the media as spies or agents stirring up turmoil.

Amy Austin Holmes, a professor of sociology at the American University in Cairo, knows several foreign colleagues who have been arrested or barred from entering Egypt because of their work. Most, she said, keep quiet to avoid antagonizing authorities.

"They think if they don't make a fuss, they'll get a visa next time. That's why people aren't even aware that there is a pattern here," she said. "It's a shame since it's creating holes in research that have ripple effects across disciplines. It's like there's a campaign to erase recent history."

Egypt has been rocked with turmoil since the 2011 uprising that ousted longtime autocrat Hosni Mubarak. An Islamist president was elected but then overthrown by the army in 2013 amid mass protests against him. Finally, general-turned-President Abdel-Fattah el-Sissi was elected, promising to bring stability.

Under el-Sissi, authorities have waged crackdowns against Islamists, then left-wing activists and finally against broader dissent. Anyone voicing criticism can come under condemnation in the media, harassment or prosecution by authorities or detention — or even forced disappearances. Rights groups have documented hundreds who have disappeared, most of them later turning up in police custody, though police deny the practice takes place.

In an open letter, some 4,600 prominent academics demanded Egyptian authorities investigate not just Regeni's death but all cases of forced disappearances. The Middle East Studies Association — one of the most prominent bodies of scholars studying the region — said in a toughly worded statement that "The growth of violence and repression against academics and associated researchers in Egypt has now reached its tragically predictable outcome with (Regeni's) murder."

Some academics, whether Egyptian or foreign, whose work is politically sensitive say they have faced intimidation in multiple ways large and small.

Last year, French graduate student Fanny Ohier was arrested in the coastal city of Damietta around the time of the anniversary of the July 3, 2013 overthrow of Islamist President Mohamed Morsi. She was doing research on the April 6 movement, a pro-democracy group that was prominent in the 2011 uprising but has since been banned.

She said a dozen security agents entered her hotel, took her to the local police station and then to Cairo, where she was told to immediately buy a ticket back to Paris or spend time in a cell before being deported.

"They didn't even let me stop at my apartment to pick up my things — I left with only my book bag after spending a night in the airport's deportation hall," she said. "To this date I've had no official explanation — they've just answered with silence."

Kholoud Saber, an Egyptian psychology assistant lecturer at Cairo University and human rights activist, was on a leave in Belgium, starting a 4-year Ph.D. program — with the required approval from her university — when she was abruptly told her leave was revoked and must return home or lose her job. She told the AP that she was told unofficially that security officials were behind it. After filing a lawsuit and sparking a solidarity campaign, Saber was just as suddenly informed she could continue her Ph.D.

Researchers in a range of topics have met troubles. Some are connected to rights issues or any subject seen as sensitive by authorities. In January, Amel Grami, a Tunisian professor of women's rights, was detained at the airport and deported as she arrived to attend a conference.

Regeni was focused on labor topics, including street vendors and independent trade unions — which often engage in strikes and are a constant worry for the government. He had told friends he was unnerved and feared he was under surveillance after someone took his picture at a labor meeting he was attending.

Hoda Kamel, who handles the labor file for the Egyptian Center for Economic and Social Rights, said she took Regeni several times to meet street vendors and introduced him to organizers from the sector. She fears his case will intimidate others.

"How could anyone from outside come here now?" she said. "You can never guess the security forces' next move. That's why it's so dangerous."

The labor sector appears to be particularly fraught with problems for researchers.

Marie Duboc, a French national, was denied entry in September 2011 even though she had already signed a contract with the American University in Cairo as an assistant sociology professor and her husband was already working at the university. She waited 12 hours at the airport with her three-month-old baby before being sent back on the next flight.

"As is the pattern in all these cases, no explanation was given," she said. The only reason she said she could imagine was her previous research on labor strikes in the textile sector under Hosni Mubarak's rule.

"I can't imagine that Ph.D. supervisors would encourage their students to conduct fieldwork" in Egypt, she said.

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Associated Press writer Sam Magdy contributed to this report.