President Nicolas Sarkozy said on July 13 he had a "burning worry" for the fate of 78-year old Michel Germaneau, who has been held since April 22, when he was seized in northern Niger near the desert border with Mali and Algeria.

Military sources in Niger said several regional leaders were involved in negotiations to win Germaneau's freedom.

Al Qaeda in the Islamic Maghreb (AQIM) had given France 15 days from July 12 to arrange a prisoner exchange and said Sarkozy would be responsible for Germaneau's life.

"(Our team) is mobilized to come to the help of our citizen," a French Foreign Ministry spokeswoman told reporters without specifying what was being done to secure his release.

The retired engineer had worked in the Algerian oil sector.

The official said France would remain discreet on the matter to ensure success.

AQIM released a picture and audio of Germaneau in May in which he said he had a serious medical condition, and urged Sarkozy to find a "good solution" for him.

The Niger military sources said they had no information on the whereabouts of the Frenchman, but that leaders across the region, including Libya's Muammar Gaddafi and Burkina Faso President Blaise Compaore, were playing a role in negotiations.

"It's true that the ultimatum is nearing, but I'm certain diplomacy will prevail," said a Niger army officer. "Mali's head of state is fighting for that and he is being helped by a few of his regional counterparts." France has previously launched military operations to save hostages. Last year, navy commandos intervened to rescue tourists kidnapped off the coast of Somalia.

This month Mali invited Algerian forces to pursue into its territory Al-Qaeda insurgents sought for the killing of 11 Algerian paramilitary police. It is not clear whether Algeria has taken up the offer.