Jurdan Martitegi, believed to be the latest military chief of ETA, has been detained in Perpignan, France, during a joint operation by French and Spanish police.
Two other suspected ETA members were detained along with Jurdan Martitegi and all three are said to have been armed, although they did not put up a fight.
Jurdan Martitegi took over as military chief of ETA after the arrest last December, also in south-west France, of Aitzol Irionda. He, in turn, had taken over from Mikel Garikoitz Aspiazu Rubina, also known as Txeroki, who had been arrested in October, again in France.
Earlier in the week, on Thursday, a female member of ETA, Itxaso Legorburu Madinabeitia, was arrested in the central French town of Mezieres-en-Brenne.