Al-Qaeda's North African wing claimed responsibility on Friday for the kidnapping of Frenchman Michel Germaneau who was seized in northern Niger in April, the US-based SITE Intelligence Group said.
SITE, which monitors Islamist websites, said Al-Qaeda in the Islamic Maghreb (AQIM) had posted an audio message from Germaneau, his picture and a copy of his identification card.
The militants demanded a prisoner exchange and said French President Nicolas Sarkozy would be responsible for the life of the captive, SITE said in its report.
AQIM said Germaneau, who was captured in the Sahara desert region on April 22, was a retired engineer who had worked in the Algerian oil sector.
Military sources in Niger have said an Algerian driver seized with Germaneau had been freed and found wandering through the desert in Mali in late April.
Governments have little influence in the desert region where bandits, smugglers, former rebels and groups linked to al Qaeda operate.
Western countries say if action is not taken, al Qaeda militants could turn the Sahara into a safe haven along the lines of Somalia or Yemen and use it to launch attacks.
Mali, Niger, Algeria and Mauritania have launched a joint military headquarters in southern Algeria which will triple the number of troops at its disposal to 75,000 within two years.