Col Bacar is on trial for illegally entering French territory
France has rejected a request for asylum by the ousted rebel leader of the Comoran island of Anjouan, Colonel Mohamed Bacar.
Comoran and African Union (AU) troops ousted Col Bacar in March, and he is in military custody on the French island of Reunion in the Indian Ocean.
Comoros and the AU have asked Paris to extradite him to face justice.
The secretary of state for overseas affairs said France would support the Comoran government's efforts.
"We will continue to act in consultation with the Comoros so that the law can be applied and Col Bacar can be tried," Yves Jego said.
But the French refugee office ruled that the ousted leader cannot be sent back to Comoros because of the risk of persecution.
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 in 2007.
He fled to the French island of Mayotte before he was transferred to Reunion and placed in custody.
Col Bacar is on trial for illegally entering French territory and possession of weapons.
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.