A French-backed operation by Mauritanian soldiers failed on Thursday to free an elderly French aid worker from the desert base of his kidnappers, members of the Al-Qaeda in the Islamic Magreb (Aqim). The French defence ministry confirmed Friday it had offered "technical and logistic" support in the search for 78-year old Michel Germaneau.

Germaneau, who was captured in late April, near Niger's borders with Algeria and Mali, was scheduled for execution two weeks ago. Since then, his captors have refused to communicate with French authorities or hand over an audio recording and photo to prove he is still alive.

Aqim, the north African affiliate of Osama bin Laden's Al Qaeda, had previously requested the release of its members in the region in exchange for Germaneau.

No signs of the French hostage were found during the raid in an undisclosed region of the Sahara, during which serveral "armed terrorists" were killed or wounded, according to an official Mauritanian source.

The Mauritanian defence department said the operation had also been conducted in order to pre-empt an Aqim-planned attack against Mauritania.

Malian security forces confirmed that they had authorised the operation, which involved the passage of planes in the northern part of the country.

The French hostage, a retired engineer who worked in the petrol industry in Algeria, is said to be in bad health. At the time of his kidnapping, Germaneau had been working with the Enmilal aid group to improve schools and health services in Sahel county, northern Niger.

According to El Pais, Madrid is concerned for the lives of two Spanish nationals, who have been held in captivity by Aqim for almost eight months.

The Islamist group executed British hostage Edwin Dyer one year ago.