Police found a large cache of explosives and arms and detained two people, including an alleged member of the Basque separatist group ETA, on Sunday.
The cache was found in Saint-Michel, in Basque country in southwest France, police said.
There were no immediate details about the two people arrested other than that one was a suspected member of ETA.
ETA stands for Basque Homeland and Freedom. It has been fighting since the late 1960s to carve an independent Basque homeland out of a region straddling northern Spain and southwest France. It has claimed responsibility for more than 800 killings.
It is classified as a terrorist group by Spain, the United States and the European Union.