An investigative judge on Friday jailed seven suspected jihadists in a case involving alleged discussions about targeting a Jewish bookstore in Barcelona.
Other potential targets of the group included synagogues and public buildings in the Catalonia region, the magistrate said in a report after receiving information from prosecutors.
The cell also planned to behead a person on a public street similar to a 2013 London attack, media reports said, citing prosecutors at the National Court.
Members of the cell planned to place the victim in an orange jumpsuit like the Islamic State militant group and kill the person in front of cameras, the EFE news agency and other media reported.
The Spanish cell, which was led by a hairdresser, also planned to kidnap a bank director and demand a ransom and had recruited for Islamic State in Catalonia, the reports said.
Authorities seized a grenade, knives, shotguns, ammunition and chemicals that could be used for bomb-making during searches that followed 11 arrests Wednesday in the northeastern Catalonia region, Judge Santiago Pedraz said in a report. It was released after the seven appeared before him in closed-door court sessions.
The suspects, mostly from the city of Terrassa about a 30-minute drive from Barcelona, had formed a group they called "Islamic Brotherhood for Jihad Predication" that was linked ideologically to the Islamic State group, the report said.
Three of those arrested were released by Pedraz and a 17-year-old suspect identified as a Paraguayan living in Spain for eight years was sent to a juvenile detention center. Six of the seven jailed adults were men with Spanish citizenship; the seventh was a Moroccan woman.
One of those ordered jailed allegedly had discussions with others about being ready to attack the bookstore with help from a neo-Nazi acquaintance, the report said.
Images of a central Barcelona hotel, a police station and a shopping center were found on the cellphone of the man who talked about the bookstore.
Catalonia regional police had been monitoring members of the alleged group for more than a year.
Paraguayan Interior Minister Francisco de Vargas said Friday that authorities were concerned about learning that a youth with Paraguayan roots had been implicated.
There were no indications that he came into contact with any extremist groups in Paraguay when he was younger, Vargas said. But Paraguayan authorities decided as a precaution to step up patrols in the so-called Triple Border part of Paraguay that borders Argentina and Brazil.
The Triple Border region is known as a smugglers haven with a large Arab community. U.S. officials have said it is a center for terrorism financing, a claim denied by the three South American nations.