A former leader of the banned Basque separatist party Batasuna was released from prison on Saturday, having served a 15-month sentence for glorifying terrorism.
Otegi called for a process of dialogue between separatists and the government
Arnaldo Otegi, 50, was met by dozens of supporters as he left the jail in the northern coastal town of San Sebastian.
"There is an unresolved problem in this country," Otegi told reporters. "I personally consider this problem will only be solved through dialogue and negotiation."
Otegi also said that during the process "all Basque political prisoners must be freed."
While serving his sentence Ortegi reportedly kept a low profile, spending his time learning English and only having rare visits from political figures. Asked what he had planned for the future, he said only, "We'll see."
He was imprisoned following a failed appeal against charges of glorifying terrorism in a speech praising a member of ETA, the Basque separatist group.
Otegi's detention in June 2007 came days after ETA called off a ceasefire with the Spanish government. He is believed to have been a key figure in the resumption of violent attacks against the Spanish state.
Batsuna has been banned since 2003 for refusing to formally sever links with ETA, which has waged a 40-year terror campaign for Basque independence in which 823 people have died.