Police suspect Basque separatists (search) were behind the theft of several tons of chemicals that could be used to make bombs from a factory in western France, judicial officials said Saturday.

Armed men wearing masks stole some 4.4 U.S. tons of sodium chlorate from a fertilizer plant in the western town of Saint-Benoit (search) on Friday, the officials said on condition of anonymity.

Investigators suspected the armed Basque separatist group ETA was involved, the officials said, adding that a factory guard told investigators that the six men spoke with Spanish accents.

Sodium chlorate has been used in the past to make bombs for ETA attacks. The chemical, normally used as a weed-killer, has been found in several ETA-related arrests in France.

ETA (search), which stands for Basque Homeland and Freedom, 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 been blamed for more than 800 killings.