An Algerian driver has been accused in Niger of complicity in the kidnapping of French tourist Michel Germaneau.
The driver was abducted along with Mr Germaneau in a remote part of northern Niger close to the border with Mali and Algeria in April, but later released.
He has now been returned to a prison in Niger, where he has been charged, sources have told Reuters news agency.
Al-Qaeda in the Islamic Maghreb (AQIM) claims to be holding the Frenchman. It has seized several tourists recently.
The US is currently conducting a military training exercise in the region to help countries such as Mali, Niger and Mauritania tackle al-Qaeda.
The kidnapping of 78-year-old Mr Germaneau and his driver near Tiguidan Tessoun happened just days after the four Saharan countries opened a military base in Algeria to counter AQIM.
A few days after the kidnapping the driver was found wandering around in the Malian desert by camel riders and returned to Algeria.
AQIM is believed to earn money from ransom payments for hostages, although this is never officially confirmed.
It has also demanded the release of some of its captured militants in exchange for hostages.
In February, Mali freed four militants, sparking a row with Mauritania.
Mali's government denied accusations it was giving in to the militants' demands and said the men had served their time.
Two Italians were freed in Mali in April after spending four months in captivity, but two Spaniards are still being held hostage.
Last year, AQIM killed a British hostage, Edwin Dyer.
The group emerged in early 2007, after a feared militant group, the Salafist Group for Preaching and Combat (GSPC), aligned itself with Osama Bin Laden's international network.
It has waged a campaign of suicide bomb attacks and ambushes in Algeria, and in recent years has become more active in the Sahara Desert, where governments struggle to impose their authority and gangs of smugglers, bandits and rebels operate alongside the militants.