The event, in the Basque capital of Bilbao, was attended by several high-ranking regional politicians and celebrities such as Pilar Bardem, mother of the Oscar-winning actor Javier Bardem, and former UNESCO Secretary-General Federico Mayor Zaragoza. No violence was reported.

Organized by a nonviolent civil initiative for prisoners known as Herrira, the protest carried the slogan "Human rights, resolution, peace. Basque prisoners back home." Some protesters waved Catalan flags in solidarity with the northeastern Spanish region that often, too, entertains the idea of independence.

As part of an amendment to a 1975 anti-terrorism law, Basque separatists are dispersed to prisons across Spain and France to make it more difficult for them to communicate with one another. Herrira has demanded that the more than 700 ETA prisoners currently spread far and wide be jailed in the Basque country to make it easier for their relatives to visit. Only about two dozen of the 700 are currently imprisoned in the Basque region of Spain.

ETA fought an armed campaign for an independent Basque homeland from 1959 until 2011, when the group announced that it would lay down its arms. The group has yet to surrender its weapons or dissolve its leadership.

However, Spanish authorities believe the group to present a minimal threat now.

mkg/hc (AP, dpa)