“We celebrate our common victory against terrorism with mixed feelings,” said French Prime Minister Edouard Philippe at a ceremony to highlight both countries' anti-terror cooperation, after ETA disbanded in May.
In a symbolic act, the French government handed over 8,000 ETA documents seized in France that could help solve more than 350 unresolved crimes committed during decades of killings, kidnappings and extortion waged for an independent Basque homeland.
“France was used as a rear base… by ETA's terrorists and had been fighting its members on its soil for many years,” Philippe said.
Until the early 1980s, France had been accused of being lenient on ETA members who had taken refuge on its soil.
Philippe said the documents would help “feed the work of historians, the work on memory, but also pursue probes of crimes that remain unresolved”.
Spanish Prime Minister Pedro Sanchez said peace was achieved “thanks to the determination of all of society and cooperation between Spain and France”.
At least 829 died at the hands of ETA in its four decades of activity.
On the other side, some 62 deaths are attributed to para-police anti-ETA death squads or far-right groups.
Two former Spanish Socialist prime ministers, Felipe Gonzalez and Jose Luis Rodriguez Zapatero, took part in the ceremony.
The former conservative prime ministers Jose Maria Aznar and Mariano Rajoy declined to attend, according to Sanchez's office.
ETA called a permanent ceasefire in 2011, and announced it was disarming in April 2017.
Waging attacks and kidnappings, the organisation tried and failed to achieve an independent Basque homeland.
It was finally brought down by scores of arrests within its ranks and rejection from a majority of the population.
READ MORE: After years in jail, ex-ETA militants still root for independence