The tortoises are prized in Asia where they are used in traditional medicine and their shells turned into jewellery.

The officers were also carrying smuggled gems and vanilla pods when the plane arrived in Reunion from the Madagascan capital Antananarivo, less than an hour's flight away.

Reunion, a French territory, was not the likely final destination of the contraband, officials said.

"The three were on a routine visit of French-Madagascan military cooperation," said an official at the French embassy in Madagascar.

"The Reunion authorities have launched an inquiry into the smuggling and where the cargo was destined to go."

The Spider and Irradiated tortoises are two of the most endangered species in Madagascar, an island larger than France that is home to 200,000 species of plants and animals found nowhere else.

Conservation groups say Madagascar's tortoises are severely endangered by habitat loss and poachers, who hunt the animals and sell the valuable parts on international markets. The tortoises are particularly prized in Japan and Thailand.

"The liver is cut out and sold as traditional medicine in Asian countries, the shell is made into jewellery and the skin used for handbags," said Lanto Andrianampianina of the local office of the New York-based Wildlife Conservation Society.

Often, the remaining parts of the tortoises are discarded because of local taboos against eating them, he said.

Madagascan police acknowledge that wildlife smuggling is a thriving business.