CAMBO-LES-BAINS, France (Reuters) - Mediators called on Friday for talks to address remaining issues linked to the dissolution of separatist group ETA, including the status of prisoners, but Spain said it would not relent on jail conditions for convicted former militants.

Jonathan Powell delivers the Arnaga Declaration alongside Cuauhtemoc Cardenas, Irati Agorria Cuevas, Bertie Ahern, Anaiz Funosas and Gerry Adams at the International Event to Advance in the Resolution of the conflict in the Basque Country, following Armed Basque separatists ETA announcement of their dissolution in Cambo-Les-Bains, France May 4, 2018. REUTERS/Vincent West

ETA declared its final dissolution this week, ending Western Europe’s last major armed campaign but leaving behind resentment after a 50-year drive for an independent Basque state that killed some 850 people.

“We believe that building peace requires political dialogue among all the key actors. To resort to security measures and prison alone rarely proves successful,” said former British government aide Jonathan Powell, reading from a statement that was also delivered in the distinct Basque language, French, and Spanish.

Gathered in Cambo-les-Bains, a town on the French side of the Basque Country, the mediators acknowledged the 305 former ETA members who are currently in jail in Spain and France.

“Deep wounds remain. Families and communities are still divided,” said Powell, who was involved in the mediation.

The status of the prisoners, some of whom are held in facilities hundreds of miles from their families, has become a bone of contention between Madrid and the Basque government.

As the ceremony was underway, Prime Minister Mariano Rajoy said Madrid would keep investigating the roughly 350 still-unsolved crimes attributed to ETA and sentences will continue to be served.

“There has never been and there never will be any impunity,” Rajoy said in a televised speech.

The head of the Basque regional government, Inigo Urkullu said this week that Rajoy had been receptive to moving prisoners closer to home, as ETA’s dissolution had always been the condition for changing policy.

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“It is a response to what most of Basque society has called for,” he told El Pais newspaper on Thursday.

Rajoy’s minority government relies on the Basque National Party (PNV) to pass measures in parliament.

But government spokesman Inigo Mendez de Vigo said on Friday Madrid would not change its policy on prisoners.

“It’s clear that the government won’t modify its penitentiary policy,” de Vigo said at a news conference when asked if Madrid could change its stance.

Family members and other supporters of the prisoners have lobbied for years for prisoners to be moved, and for those who have fallen ill to be released.

Neither Spain nor France sent a government representative to the meeting, which was attended by the former of the Irish nationalist party Sinn Fein Gerry Adams and Ireland’s former prime minister Bertie Aherne.

Last month, ETA apologized to its victims and their relatives. About 850 people, including police, politicians and ordinary citizens, were killed in ETA bombings and shootings across Spain.

ETA was formed in 1959 by students angry at the repressive dictatorship of General Francisco Franco but carried out its first known killing in 1968. Its campaign included political assassinations, most notably of Franco’s chosen successor, Luis Carrero Blanco in 1973.

But as Spain returned to democracy after Franco’s death in 1975 and the Basque Country gained a large measure of autonomy, its attacks on the general populace, including a 1987 car bomb at a Barcelona supermarket which killed a pregnant woman and two children, horrified people and cost it support.

Crackdowns by Spanish and French police also weakened it.

Its demise comes as the Spanish government grapples with another separatist movement in the northeastern region of Catalonia. Although that is a non-violent campaign, it has brought on Spain’s most serious constitutional crisis in four decades and a government crackdown on its leaders.