Police sources confirmed to Efe news that the 12 detainees formed the nucleus of a group of about 80 people who were attempting to block the entrance of the High Court of Justice of Catalonia to demand freedom for former regional Vice President Oriol Junqueras.
Junqueras faces charges of rebellion and sedition for his role last year in a referendum and subsequent declaration of independence deemed illegal by Spain.
The protest was called by the Committees for the Defence of the Republic, a network of groups of volunteers that aim to protect and uphold the region's declaration of independence.
Police were seen carrying huge bolt cutters and trying to prise the activists away from their post. A majority of the protestors were sitting on the steps with some holding guitars or wearing clown noses, alongside a sign that urged people to "stop the coup d'etat".
The sign referred to the Spanish state's application of Article 155 of the Constitution, which saw the region's autonomy rolled back, its government dissolved and fresh elections called, a move which some pro-independence hardliners saw as an attack on a fledgling sovereign republic.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
