The accusations have created a storm in Islamic and academic circles across Europe. Mr. Ramadan is a grandson of Hassan al-Banna, who founded the Muslim Brotherhood in Egypt in the 1920s. He is the author of a dozen books in English on modern Islam and the Western world, and a familiar presence on television news shows and on social media.

Mr. Ramadan has said that the accusations are unfounded and has vowed to fight the cases in court. He has filed a defamation suit in Paris against one of his accusers, the French activist and author Henda Ayari.

Ms. Ayari accused Mr. Ramadan of raping and assaulting her in a hotel on the sidelines of a conference in Paris in 2012. She said Mr. Ramadan had acted as an online teacher and mentor to her and then had suggested one day that they meet at his hotel.

She wrote about the encounter in a book in 2016, but did not name her attacker at the time. Last month, encouraged by the wave of denunciations by women outing their sexual aggressors in the #MeToo campaign on social media after the Harvey Weinstein scandal, Ms. Ayari identified Mr. Ramadan as her attacker. She said she had not spoken out earlier because Mr. Ramadan had threatened her and her children.

Ms. Ayari has lodged a complaint with the French police, alleging rape, sexual assault, harassment and intimidation. Her lawyers said she had also submitted evidence with her complaint.