MADRID/SALLANCHES (Reuters) - ETA kingpin Josu Ternera, described by Spain as the Basque separatist group’s most wanted fugitive, was arrested in France on Thursday after more than 16 years in hiding from authorities in both countries.

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Ternera was a long-time leader of a group estimated to have killed more than 850 people during a 50-year guerrilla campaign aimed at creating a Basque state in northern Spain and southwest France. He announced its dissolution in 2018.

Spain wants to try Ternera over accusations that he ordered the bombing of a Civil Guard barracks in the city of Zaragoza in 1987 that killed 11 people including six children.

The 69-year old was arrested in the French Alps on a separate warrant from a Paris court that sentenced him in absentia in 2017 to eight years in prison for membership of a terrorist group, a French judicial source said.

He had been on the run since 2002 when, while he was serving as a lawmaker in the Basque regional parliament, Spain’s supreme court issued an international arrest warrant against him over the 1987 attack.

The Association of the Basque Country Victims of Terrorism said it wanted Ternera to be tried for all his alleged crimes.

“Today we start on a path to dignity,” Covite president Consuelo Ordonez tweeted.

Pilar Vallarin, who lost a brother and niece in the Zaragoza bombing, told Basque Radio SER Euskadi: “We’ve lived for 31 years knowing that this guy is free and at ease.”

TAKEN TO HOSPITAL

Spain’s acting interior minister, Fernando Grande-Marlaska, said France should allow Spain to try Ternera, whose real name is Jose Antonio Urrutikoetxea, before he served his French sentence.

He also said that, as a Spanish citizen, Ternera could ask to serve his sentence in Spain.

Ternera was arrested in a joint Franco-Spanish operation in the town of Sallanches and, after asking for a doctor, was taken to hospital, a source in the French prosecutor’s office said. The Spanish news site El Pais said he had been on his way to receive cancer treatment when he was detained.

French media said it was likely Ternera would be taken to appear before a judge in the nearby town of Bonneville. A Reuters photographer saw a man, cuffed and hooded, being led out of the courthouse by plain-clothed police wearing balaclavas, to be driven away in an unmarked police car under escort.

Spain’s Interior Ministry said Ternera had been living nearby in Saint-Gervais-les-Bains, close to France’s border with Italy and Switzerland.

“Franco-Spanish cooperation has once again demonstrated its effectiveness,” Spain’s acting prime minister, Pedro Sanchez, said in a statement.

ETA (Euskadi Ta Askatasuna, or Basque Country and Freedom) declared a ceasefire in 2011 and handed over weapons in April 2017, bringing Western Europe’s last major armed insurgency to a close. Ternera announced a year ago that it had dismantled all its structures.