The wives and children of French jihadists captured in Syria have filed a legal complaint against French authorities for refusing to repatriate them, their lawyers announced Wednesday.

The question of what to do with some 40 captured jihadists -- men and women, accompanied by around 20 children, who were living under the Islamic State group -- has been hotly debated in recent weeks.

The French government said on January 4 that those detained in Kurdish-held areas of Syria -- the vast majority of the cases -- should be left there so long as they can be guaranteed a fair trial.

But their lawyers argue that France has a duty to repatriate its citizens.

"These women who went out there are the object of legal proceedings in France," lawyers Marie Dose, William Bourdon, Martin Pradel and Marc Bailly said in a statement.

"They accept that they must face up to their criminal responsibilities as soon as they arrive on French territory."

By leaving them there, French authorities are "additionally exposing these mothers and children to obvious risks -- notably in terms of their health, in a warzone."

The families have filed a legal complaint against French authorities for arbitrary detention and abuse of authority, the statement said.

Their lawyers argued that Syrian Kurdistan is not a legally recognised state and so "these women and children are being held in unauthorised detention".

The vast majority of jihadists detained in France are being held by Kurdish forces in Syria, according to a source close to the case.

The lawyers had yet to specify how many families were involved in the suit.

But they are not believed to involve the most prominent Frenchwoman in Kurdish detention, the notorious Islamic State propagandist Emilie Konig, a 33-year-old Muslim convert from Brittany.

Konig, who features on UN and US blacklists of dangerous militants, was captured last month and is being held in a Kurdish camp with her three young children along with several other French women.

Her lawyer Bruno Vinay has said previously she has requested to be brought to trial at home in France.