French police said they arrested the suspected military leader of the Basque separatist movement ETA in the southwestern town of Bayonne on Thursday.
Spanish national Mikel Kabikoitz Karrera Sarobe, known as Ata, was detained along with another man and a woman during a raid on an apartment, police said. Police also found weapons in the apartment and said the people did not resist their arrest.
He has been considered the military leader of ETA since French police arrested his predecessor Ibon Gogeascoechea in February.
ETA guerrillas active in Spain often take refuge in southwest France, areas of which they claim as part of the Basque homeland. The group has killed more than 850 people in Spain in recent decades.
The group is suspected of being behind the murder of French policeman Jean-Serge Nerin near Paris in March -- the first French security official to be killed by ETA.
After the killing, French President Nicolas Sarkozy vowed to get rid of all ETA bases and to hunt down its supporters.
The arrests were made after a joint investigation by the DCRI French interior security services with the Spanish Guardia Civil and Spanish intelligence service.
Police said a second man arrested was Arkaitz Aguirregabiria del Barrio, 27, who they described as a very violent high-ranking ETA member. Police suspect he was present when the French policeman was killed.
Nerin, 52, was shot while investigating reports of a car theft at a car lot in Dammarie-les-Lys. He and other officers came under fire from people, including a woman, in a second car after they stopped a first car.
A fourth suspected ETA member, of French nationality, was arrested on Thursday in the village of Urrugne, close to the coastal town of Saint-Jean-de-Luz in French Basque country.
The Spanish Interior Ministry named the other arrested person as Maite Aranalde Ijurco and Benoît Aramendi. The girlfriend of Aramendi, Laettitia Chevalier, was also detained.
French and Spanish authorities have arrested several senior ETA members since 2008. Spain's Interior Ministry says Spanish and French police have arrested 50 ETA members this year alone.