Spanish police have arrested at least 10 suspected members of groups outlawed for their links to the armed Basque Group ETA, the Interior Ministry said.
Officials said most of the arrests were carried out early on Tuesday morning in the northern region of Navarra, next to the Basque region.
The detainees are believed to be members of two civic groups, Ekin and Askatasuna, both regarded as support organisations for ETA.
The arrests come just over a week after ETA announced a permanent ceasefire.
The Spanish government insists ETA must disband and lay down its arms. It says it will maintain police attention on the group and its supporters until then.
ETA has killed more than 825 people since the 1960s in its campaign for an independent Basque state.