Sinn Féin president Gerry Adams has welcomed the announcement by Eta of a permanent ceasefire.
Mr Adams said the announcement "provides all sides to the conflict with an opportunity of historic proportions".
"Today's announcement gives a considerable boost to the development of a conflict resolution process. He added: "It is incumbent on all sides to the conflict to grasp this opportunity, and to do everything in their power to make political progress a reality.
"The Spanish government should immediately intervene to stop the political trials against Batasuna leaders, including Arnaldo Otegi."
Otegi has served jail terms before and is free on bail of €400,000 while the high court prepares a case against him. Prosecuters want him to answer new charges of "various criminal acts" following Eta bomb attacks earlier this month.
Eta has killed about 800 people since 1968, in its fight for an independent Basque state straddling northern Spain and southwestern France. The group, branded terrorists by the EU and the United States, has not killed anybody since 2003.