Col Bacar (c) was re-elected president of Anjouan in disputed polls last June
The deposed rebel leader of the Comoran Island of Anjouan has been remanded in custody on the French Indian Ocean Island of Reunion.
Mohammed Bacar appeared in court after an extradition request was received from the Comoran authorities, a Reunion prosecutor said.
The rebel leader was ousted last week after an invasion of Anjouan by Comoran troops backed by African Union forces.
Col Bacar had originally fled to the island of Mayotte seeking asylum.
But his presence on Mayotte sparked disturbances, and the French military flew him and 21 people with him to the larger Island of Reunion.
"This detention follows a request to the French government by the Comoros justice minister for [his] arrest with the aim of extradition," said Reunion deputy prosecutor Jean-Robert Dobanton.
A lawyer representing the detained men condemned the decision.
"The accusations against my clients have not been given in detail and refer to no date, place or victim," said the lawyer, Marie Briot.
The Comoran government and the AU had asked Paris to extradite Col Bacar to face justice amid anti-French protests in the Comoran capital, Moroni.
Police had used tear gas to disperse hundreds of demonstrators near the French embassy in the town last week.
The operation against Col Bacar was launched after he refused to step down as president of Anjouan, and accept the authority of the federal government after a disputed election last June.
About 600 Comoran and AU troops took part in the amphibious assault on 25 March.
The Comoros archipelago in the Indian Ocean has had a fractious history since independence from France, experiencing more than 20 coups or attempted coups.
The three main islands of the archipelago - Grand Comore, Moheli and Anjouan - lie 300km (186 miles) off Africa's east coast, north of Madagascar.
The island of Mayotte is the only one of the Comoros islands to have opted to remain French when the other islands gained independence in 1975 - but it remains a source of contention with both countries claiming sovereignty.