An investigative judge on Friday jailed seven suspected jihadists in a case involving planned possible kidnappings, an execution and attacks on Jewish shops and public buildings in Spain.

Other potential targets allegedly included synagogues, commercial centers, police and security forces and the Catalan regional parliament.

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.

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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.

Authorities said the cell had already sent at least four recruits to Syria and Iraq, where the IS declared a “caliphate” last year.

A source in the investigation said the suspects appeared to have been radicalized “very quickly”.

“They were considering abducting a person in Spain, dressing them in an orange overall in the style of the group known as Islamic State, interrogating them and cutting their throat in order to broadcast it” by video, a source in the investigation told AFP.

The IS has frequently broadcast footage showing their execution victims wearing orange suits of the same style given to prisoners at the controversial US military prison in Guantanamo Bay.

Gang members had also discussed “abducting the director of a bank branch” for ransom, the source added.

Police investigations revealed that the suspected cell founder, Antonio Saez Martinez — dubbed “Ali the Hairdresser” — told other members he came close to launching an attack on a Jewish bookshop in Barcelona, Judge Pedraz wrote.

He allegedly proposed attacks with guns and grenades against synagogues, security forces and the Catalan regional parliament.

Police found on his mobile phone photographs of potential targets for attacks in Barcelona such as a hotel, a police station and a shopping centre, the ruling 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. US officials have said it is a center for terrorism financing, a claim denied by the three South American nations.

Spain stepped up counter-terrorism operations after jihadist attacks killed 17 people in Paris in January.

Spanish authorities have arrested around 40 suspected jihadists so far this year — five more than in the whole of 2014.