Ali Charaf Damache, who holds both Algerian and Irish nationality, was detained yesterday in Barcelona, said Jordi Jane, who heads interior matters for the regional government.
"Regional police located and detained an alleged jihadist who was the subject of an international search warrant issued by Interpol US," he told reporters.
US officials say Damache worked with Colleen LaRose -- a Pennsylvania woman who converted to Islam and took the name Jihad Jane and others to create a "violent jihad organisation" with men and women from Europe and the United States.
US authorities say Damache and others recruited men online "to wage violent jihad in South Asia and Europe" as well as women with passports and the ability to travel to and around Europe in support of their plots.
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According to a judge at Spain's national court, the Audiencia Nacional, Damache had initially been detained in Ireland where he was living, but a court there refused a US request to extradite him and he walked free.
He has refused to be extradited to the United States, where he faces up to 45 years in prison if convicted, and has been remanded in Spanish custody until a local court decides on his fate.