Jean-Yves Le Drian Mali
France\'s Defence Minister Jean-Yves Le Drian speaks to a French soldier at a French military encampment at a Malian air base in Gao (Reuters)

France has captured two of its own citizens who were fighting alongside Islamist rebels against Paris-led troops in northern Mali, defence minister Jean-Yves Le Drian has said.

A 25-year-old Franco-Malian man was taken prisoner during fighting in the region and is about to be extradited to France, Le Drian told Europe-1 radio.

The second man, a 35-year-old of French-Algerian origin, was arrested by Malian police and has already been flown back to France.

"This shows there was [in Mali] a terrorist structure able to accommodate young people with radical ideas, as already happened in Afghanistan and Syria," Le Drian said.

Authorities believe about a dozen French citizens travelled to Mali to join the extremists, after terrorists took over the north of the country last year.

France's Mali campaign, Operation Serval, also aimed to prevent the creation of a jihadist haven where such radicals could be trained to potentially come home with skills to stage terrorist attacks.

DNA tests

Meanwhile, French Foreign Minister Laurent Fabius said DNA tests are being carried out to cast doubts over the identity of some terrorists killed in northern Mali.

"We know that there are many leaders among the hundreds of terrorists killed during this operation," Fabius told RTL radio.

"Regarding details about the identity of two or three leaders cited [Zeid and Belmokhtar], precise DNA verification has to be carried out."

Mystery has surrounded the faith of two Islamist leaders, Mokhtar Belmokhtar and Abdelhamid Abou Zeid, who were reportedly killed by Chadian troops backing French forces in the region.

Chad's President Idriss Deby announced the Islamist leaders were killed in two separate raids earlier this month, but no supporting evidence was presented.

The death of Belmokhtar, the mastermind behind a devastating raid on an Algerian gas plant in January, was denied by al-Qaeda in the Islamic Maghreb (Aqim), although the organisation did confirm the killing of its second-in-command Zeid

Dubbed "The Uncatchable"or" Mr Marlboro", Belmokhtar is a former Aqim member and is on the wanted list for his role in the In Amenas gas plant siege in which 37 people, including six Britons, were killed.

A photo of what was said to be Belmokhtar's body was published by French state-funded Radio France Internationale (RFI).

However Belmokhtar wasn't easily identifiable, since the photo actually depicted a Chadian soldier's mobile phone image of a corpse.

Earlier this week Le Drian said he could not confirm the death.

"I have a lot of respect for President Deby," Le Drian told France 2 television. "But the minister of defence has no evidence.

"I'd love to say it but I am not going to say anything because I don't know," Le Drian said.