Islamic scholar Tariq Ramadan was detained by French police on Wednesday, several months after two women filed rape charges against him, a legal source said.
Mr Ramadan was called in for questioning at a Paris police station and taken into custody "as part of a preliminary inquiry in Paris into rape and assault allegations", the source told AFP.
The prominent Oxford professor, who is the grandson of the founder of the Muslim Brotherhood in Egypt, had taken a leave of absence from his teaching post at the prestigious university after a wave of rape and sexual assault allegations last autumn.
The first complainant, French writer Henda Ayari, says Mr Ramadan raped her in a Paris hotel room in 2012.
Ms Ayari, 41, who lodged a rape complaint against the 55-year-old Swiss national on October 20, claimed that for Mr Ramadan, "either you wear a veil or you get raped".
"He choked me so hard that I thought I was going to die," she added.
She said she was encouraged to speak out against him publicly by the "Me Too" campaign sweeping the world.
"It was the #BalanceTonPorc campaign that pushed me to reveal his name," she said, in reference to France's version of the hashtag which means "Expose your pig".
Mr Ramadan is also accused of raping another woman in a hotel room in 2009. The unnamed 42-year-old, who is reported to have disability in her legs, said in October that the professor had subjected her to a terrifying and violent sexual assault.
She also filed a formal complaint against him, in which she described her battle with depression and her attempt to commit suicide following the attack.
Mr Ramadan has denied the allegations and filed a complaint for slander against Ms Ayari.
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A third woman told Le Parisien in an interview in October that Mr Ramadan sexually harassed her in 2014.
The woman, identified as Yasmina, said Mr Ramadan blackmailed her for sexual favours, threatening to distribute "compromising pictures" of her.
All the complainants said they had initially made contact with Mr Ramadan for spiritual guidance.
In further shocking allegations, Mr Ramadan was accused of seducing four of his teenage pupils in the 1980s and 1990s when he was teaching in his hometown of Geneva.
Four of his former students described the incidents to The Tribune de Geneve newspaper, which published their stories at the start of November.
One of them claimed that he tried unsuccessfully to seduce her when she was just 14 years old. He allegedly targeted three others, who were aged between 15 and 18 years old at the time, according to the newspaper's report.
Supporters of Mr Ramadan are describing the accusations against him part of a “international Zionist plot” to destroy his name.
But other former friends have come forward to disparage him in recent months.
Stephane Lathion, a Swiss specialist in Islam who spent years accompanying Mr Ramadan on his trips across Europe, told The Tribune de Geneve that he had heard various rumours and suspicions about his former close associate's behaviour over the years.
He shared his opinion with the paper, saying: “I'm not surprised to see testimonials coming from everywhere. Not only are the reported facts shocking, but they also reveal the discrepancy between his attitude and his discourse on a moralising Islam, which advocates sexual relations in the exclusive context of marriage.”
He continued: "Tariq Ramadan is a predator who has abused his power as a teacher, preacher and intellectual to seduce women and girls, who have suffered.”