The European Court of Human Rights on Monday condemned Spain over the prolonged detention of an ETA militant and ordered her rapid release.
The decision upheld the Strasbourg-based court's previous ruling concerning Ines del Rio Prada, a member of the Basque separatist group who has been in jail since 1989 after being sentenced to 3,000 years for terrorism-linked offences.
The court had ordered Del Rio Prada's release in July 2012 but agreed to a request by the Spanish government to re-examine the case.
However, in its ruling on Monday, the ECHR said Spain should "ensure that the applicant was released at the earliest possible date".
It ruled against Spain over a legal practice known as the "Parot doctrine" that allowed prison terms to be extended for people convicted of terrorist offences.
The doctrine, adopted by the Spanish Supreme Court in 2006, meant that years of remission earned through prison work were deducted from the total sentence -- often amounting to hundreds of years -- instead of the 30-year limit on prison terms set by Spanish law.
ETA, listed as a terrorist group in the United States and Europe, is blamed for the deaths of 829 people in a four-decade campaign of shootings and bombings for an independent homeland in northern Spain and southern France.
Many of its leaders have been arrested in recent years.
In October 2011, ETA declared a "definitive end to armed activity" but it has not formally disarmed nor disbanded as the Spanish and French governments demand.