PARIS: A Nigerian Islamist group warned against the use of force to free a French man and six members of his family kidnapped in Cameroon in a video aired on Thursday.

Tanguy Moulin-Fournier was kidnapped on February 19 along with his wife, four children aged between five and 12, and brother while vacationing in northern Cameroon.

"We are proud to say that we are holding the seven French hostages," said a Boko Haram member in the video aired by France's i-Tele channel with French sub-titles.

The man is shown holding an assault rifle and the family is shown to the left of the screen in the grainy images.

"We are holding them because Nigerian and Cameroonian authorities have arrested our members and are brutalising them and we do not know the conditions under which they are detained," the man said.

"We affirm that we will not free these French hostages while our members are being held in Nigeria and Cameroon," he said. "Force will not work in freeing them, we are ready to defend ourselves..."

Boko Haram earlier ran an audio recording of Tanguy Moulin-Fournier in which he seemingly asks Cameroon President Paul Biya to free detained members of the group.

Boko Haram is believed to include a number of factions with various interests and shifting demands.

The group has in the past called for the creation of an Islamic state in Nigeria, where corruption is deeply rooted and most of the population lives on less than $2 per day despite its vast oil reserves.