GENEVA/MADRID (Reuters) - Basque separatist group ETA said on Thursday it had completely dismantled and ended all its activity, ending a 50-year campaign of violence across Spain in which it killed about 850 people.

In Madrid, however, Spanish Prime Minister Mariano Rajoy said there would be no impunity for ETA and the government would still track down former militants.

“Whatever they might choose to do over the next few days, nothing will change the unquestionable reality: ETA’s whole project has been a resounding and emphatic failure,” Rajoy said.

In a letter read out at the headquarters of a Geneva-based conflict resolution group, ETA, founded to fight for an independent state in northern Spain and southern France, said its journey had ended.

“We have made this, our last decision, in order to foster a new historical phase,” said the letter, signed Euskadi Ta Askatasuna (ETA - Basque Country and Freedom in English).

“ETA was born from the people and now it dissolves back into the people,” said the letter, which was read out by David Harland, director of the Centre for Humanitarian Dialogue.

The center first facilitated discrete talks between ETA and the former Spanish government of Jose Luis Zapatero in 2004.

ETA announced its decision to end attacks in 2011 and in 2017 it handed over 3.5 tonnes of weapons, bringing Western Europe’s last major militant campaign to a close.

It signaled it had completely dismantled in a letter published by the Spanish online newspaper El Diario on Wednesday.

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RECONCILIATION OR PUNISHMENT?

Calling it a “bitter confrontation,” the center’s Harland also referred to the killing of ETA suspects by death squads linked to government officials.

“A long work of reconciliation now lies ahead. It will require recognition, respect, apology and support to all the victims of violence as well as a commitment to the truth and justice wherever that leads,” Harland said.

However, Prime Minister Rajoy made clear that his government considered ETA as nothing more than criminals.

“ETA won’t find a glimmer of impunity for its crimes. It can announce its disappearance but its crimes will not disappear, nor will the work of justice to track them down and punish them,” he told reporters after a speech to inaugurate a Civil Guard training center in Logrono, northern Spain.

Regional government head Inigo Urkullu said the organization had inflicted pain and suffering on the people of the Basque Country, adding he doubted it would have more than four or five lines in history books in the future.

In an interview with El Pais newspaper on Thursday, Urkullu said ETA should never have existed.

“Here we have all lost. There are no winners or losers,” he said.

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The group is due to formalize its dissolution at an official event in France on Friday. Last month, it apologized to its victims and their relatives. About 850 people, including police, politicians and ordinary citizens, were killed in ETA attacks.

ETA was formed in Madrid in 1959 by students angry at the repressive dictatorship of General Francisco Franco.

Its campaign included political assassinations -- most notably of Franco’s chosen successor, Luis Carrero Blanco in 1973 -- and bombings.

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.