The Cairo correspondent of the French newspaper La Croix was deported on Wednesday after being detained at Cairo airport two days earlier on his return from a holiday, the newspaper said.
The newspaper said Remy Pigaglio was not informed of the reason for his expulsion, which comes amid an intensifying crackdown on dissent by the administration of President Abdel-Fattah al-Sissi.
Airport officials, speaking on condition of anonymity, said Pigaglio's passport had been flagged by a security agency on the grounds that he had been involved in "activities injurious to Egypt and threatening Egyptian security," without specifying further.
La Croix's director, Guillaume Goubert, however, said the journalist's work in Cairo "should have inspired nothing but respect for his professionalism."
Egyptian authorities have launched a renewed crackdown since April, amid criticism of a decision to hand two strategic Red Sea islands over to Saudi Arabia.
Earlier this month over 150 people were jailed for between two and five years over attempted protests against the handover - although 47 of them had their sentences overturned by an appeals court on Tuesday.
Police also infuriated local journalists by raiding their union headquarters to arrest two journalists accused of publishing false news, inciting unauthorized protests and plotting to overthrow the regime.
Press freedom advocacy group Reporters Without Borders said it was "very disturbed" by Pigaglio's expulsion, adding that "everything suggests that this was designed to intimidate all the foreign correspondents based in Cairo.”
French journalists working in Cairo released a statement condemning what they said was "the growing repression (surveillance, intimidation, deportation and detention) exerted by the authorities on Egyptian and foreign media alike."
The French Foreign Ministry said France "deeply regrets" the decision of the Egyptian authorities, saying that Foreign Minister Jean-Marc Ayrault spoke to his Egyptian counterpart about Pigaglio on Tuesday. France's embassy in Cairo is advocating for Egypt to reconsider, the ministry said.
According to the New York-based Committee to Protect Journalists (CPJ), Egypt was the "second worst jailer of journalists worldwide" in 2015.
CPJ figures showed Egypt held 23 journalists at the year's end, including photojournalist Mahmoud Abu Zaid, who was arrested while covering the deadly police dispersal of Islamist protests in August 2013 and has recently been brought to trial on charges of involvement in the violence.
Three journalists with Al Jazeera's English-language channel received pardons from al-Sissi in September after being jailed for allegedly publishing false news and collaborating with Morsi's banned Muslim Brotherhood movement.