A gang of men stormed into a warehouse belonging to public works company Titanite in western France at dawn on Tuesday. One of the men spoke Spanish, police said.
They made off with eight tons of dynamite, seven miles of cable and almost 6,000 detonators. Three employees at the warehouse were tied up during the robbery, which was carried out very quickly, suggesting the gang had prior knowledge of the plant.
The thieves then drove off with the explosives in three vans belonging to the company. One of the vans was later found by police.
ETA, which wants to carve an independent homeland out of land straddling northern Spain and southern France, is a Basque-language acronym for Basque Homeland and Freedom.
Almost 800 people were killed between 1968-1998 in its campaign for an independent nation. It officially began a cease-fire on Sept. 18 but has yet to announce a definite end to the violence.