Spanish police arrested on Tuesday nine alleged members of a group linked to Basque separatists ETA.
They are said to belong to Ekin, a body that prepares and sends out directives to the armed organisation.
ETA is banned as a terrorist group by the EU and the US.
Officers from the Civil Guard made the arrests accross the Basque country and Navarra province in northern Spain.
It comes a week after ETA declared a ceasefire, following a violent and sometimes deadly campaign to establish a homeland independent from Spain that has stretched four decades.
The group made a similar announcement in March 2006, only for the violence to return in the December of that year when a car bomb at Madrid’s airport killed two people.