Four suspected members of Eta, allegedly including the armed Basque separatist group's top explosives expert, have been arrested in the French southwestern town of Cahors, police there have said.
Three men and a woman were arrested during Saturday's raid on a house that the Spanish interior minister described as an "Eta operational base."
Alfredo Perez Rubalcaba said that Luis Ignacio Iruretagoyena Lanz, an alleged bomb maker, was among those detained.
The minister described the arrests, carried out in a joint operation by French and Spanish police, as being "of enormous importance".
"Iruretagoyena is considered by the maximum expert in the making of bombs within Eta," he said at a press conference in Madrid.
Peace talks
The operation comes less than a week after the group carried out its first attack after ending its ceasefire on 5 June.
The other suspects were identified as Ander Múgica Alaitz Aramendi, Alaitz Aramendi Jaunarena and Ohian Barandalla and investigations were ongoing, the minister said.
The Spanish government had attempted to hold peace talks with Eta last year but called them off after the explosion.
The group, whose name is a Basque-language acronym for Basque Homeland Freedom, has killed more than 800 people since 1968 in an armed campaign for independence for the Basque territories in northern Spain and southern France.