Mikel Karrerra Sarobe was on a Spanish police most-wanted list
The suspected military leader of the armed Basque separatist group Eta has been arrested, French police say.
At least four suspects were held during dawn raids, including the man described as Eta's military chief, Mikel Kabikoitz Karrera Sarobe.
Reports say the three had been picked up in the south-western town of Bayonne and a fourth in a nearby village.
The group has used France as a base and five Eta leaders have been arrested there in the past two years.
Mikel Karrera Sarobe, a Spanish national also known as Ata, is thought to have taken over the key role in the organisation after the arrest of his predecessor Ibon Gogeascoechea in February.
"He is currently the most senior leader of the terrorist group, the head of its military operations, the one who gives orders to Eta commandos," said Spanish Interior Minister Alfredo Perez Rubalcaba.
Mikel Karrera Sarobe was detained with another man and a woman at a flat in Bayonne. At least one suspect was arrested near the coastal town of St Jean de Luz.
Mr Rubalcaba identified second man arrested in Bayonne as Arkaitz Aguirregabiria del Barrio, who he described as the group's number two.
Arkaitz Aguirregabiria del Barrio was wanted in France for his alleged role in the murder of a French policeman, Jean-Serge Nerin, in March.
Eta has been blamed for more than 820 deaths during its 41-year campaign in Spain. The group wants an independent Basque homeland.
It called a truce in March 2006, but it was broken by December of that year.