Prominent Muslim academic Tariq Ramadan is being questioned by French police investigating allegations of rape and sexual assault against him.
He was taken into custody in Paris over claims made by two women last year.
Mr Ramadan, 55, denies wrongdoing and is suing one of his accusers, Henda Ayari, a former radical Islamist who now heads a secular feminist group.
Mr Ramadan, a Swiss national, teaches Islamic studies at Oxford University, but took leave of absence in November.
How did the allegations emerge?
In a book published in 2016, Ms Ayari wrote about being raped in a Paris hotel four years earlier, but the book did not name the attacker.
In October 2017, she said the sexual assault scandal surrounding Hollywood mogul Harvey Weinstein had emboldened her to accuse Mr Ramadan explicitly.
"He literally pounced on me like a wild animal," Ms Ayari told French TV.
Another woman, a convert to Islam who has remained anonymous, later accused him of raping her in 2009.
Four Swiss women have also accused the scholar of making sexual advances while they were students in Geneva. He says all the allegations are part of a "campaign of slander" by enemies.
Who is Tariq Ramadan?
A controversial and influential figure among Muslim scholars, he is the grandson of Hassan al-Banna, the Egyptian imam who founded the Muslim Brotherhood in the 1920s.
Tariq Ramadan challenges Muslim fundamentalists and encourages dialogue between religions, but some critics accuse him of promoting political Islam.
Since 2009 he has been professor of contemporary Islamic studies at St Antony's College, Oxford.
He has also sat on a UK Foreign Office advisory group on freedom of religion.