Madrid  - Spanish and French police are searching for a "car bomb factory" belonging to the militant Basque separatist group ETA in southern France, Spanish press reports said Friday, two days after a car bombing killed a police officer in Spain's northern Basque region.

Juan Manuel Pinuel was killed in an attack against a barracks of the paramilitary Civil Guard in Legutiano. Four other officers were injured.

The van used in the attack had been stolen near the French city of Limoges a month earlier.

ETA was believed to have rebuilt its explosives infrastructure in France after a previous bomb workshop was dismantled, with the arrest of explosives expert Luis Ignacio Iruretagoyena in September.

ETA activists based in France apparently prepared Wednesday's car bomb, placing more than 100 kilos of explosives inside and handing the vehicle over to others on the Spanish side of the border, the daily La Vanguardia quoted police sources as saying.

Explosives prepared in France were also used in several smaller attacks recently, according to the daily El Mundo.

ETA has long had much of its infrastructure based in southern France, in an attempt to avoid Spanish police.

The group has killed about 830 people in its four-decade campaign for a sovereign Basque state. Six of the victims were killed since Spanish Prime Minister Jose Luis Rodriguez Zapatero's attempt to negotiate with ETA collapsed in December 2006. (dpa)