France has banned the director of campaign group Cage from entering the country and accused him of spreading conspiracy theories about “Islamophobic persecution”.
Muhammad Rabbani arrived in Paris last Tuesday but was detained for 24 hours before being sent back to London.
Last year the French government's anti-radicalisation body had labelled the group “Islamist militants”.
Mr Rabbani was previously barred by France until Cage overturned his ban in 2020.
In a document, the Interior Ministry said Mr Rabbani posed a threat. The ministry has also accused Cage of being part of a “radical Islamist movement” and “spreading slanderous words” about “supposed Islamophobic persecution".
“Given the particularly high terrorist threat, his presence on national territory would constitute a serious threat to public order and the internal security of France,” it said.
The move comes as France has contended with days of rioting over the fatal shooting by police of Nahel Merzouk, a French teenager of Moroccan and Algerian descent.
Mr Rabbani said he was banned due to a speech he gave at an Organisation for Security and Co-operation in Europe conference last year.
“France has banned me for delivering a speech at the OSCE conference, the world’s largest regional security intergovernmental organisation," he tweeted.
Last year France's Interministerial Committee for the Prevention of Delinquency and Radicalisation accused Cage, founded by former Guantanamo Bay prisoner Moazzam Begg, of supporting terrorists and conducting a smear campaign against France.
It alleges Cage supported the killing of French teacher Samuel Paty, who was beheaded by an extremist, and of backing Mohammed Emwazi, ringleader of an ISIS terrorist cell known as The Beatles.
Cage had previously published a report accusing France of “state-led persecution” against Muslims “on an industrial scale”.
The document accused President Emmanuel Macron's government of a four-year campaign of Islamophobia.
