Spanish police have arrested 13 suspected members of a group considered to be the youth branch of the armed Basque organisation ETA.
The arrests took place on early Friday morning in the northern Basque region and in the nearby regions of Navarra and Catalonia.
Several houses were raided by some 300 police officers in the operation which targeted Segi, an organisation outlawed in 2007.
An interior ministry statement said police believe Segi continues to be a training group for future members of ETA. It is linked to vandalism sprees against government buildings, banks and political party offices.
ETA has killed more than 825 people in its campaign for an independent Basque state straddling northern Spain and south-west France.