The growing list of suspects and multiple targets suggested the kind of coordination and planning seen in two major attacks in Paris in 2015 and another in Brussels the following year.
They said the group was led by an imam who tutored its members, mainly young Moroccans, in jihad (holy war) and told them "martyrdom is a good thing, according to the Koran", Mohamed Houli Chemlal told a Spanish High Court judge.
At Tuesday's closed-door hearing, Andreu was planned to read out charges against the men, expected to include counts of terrorism, murder and weapons possession.
One of the suspected members in a terrorist cell that carried out last week's fatal attacks in Spain told a Madrid court that a bigger plot was in the works.
Chemlal was injured in an explosion at a house in Alcanar, south of Barcelona late on Wednesday night, presumably caused by an explosion in one of the over 50 butane gas canisters they had collected over the past six months.
A second suspect was arrested in the town of Oujda, close to Morocco's border with Algeria, 2M reported.
Oukabir testified that he rented the vans used in the attacks but thought they were going to be used for a house move.
Two of them - Mohamed Houli Chemlal, 21, and Driss Oukabir, 27 - were remanded in custody and charged with terror related offences.
His brother Moussa was one of the five radicals shot dead on Friday by police in Cambrils.
The closed-door hearing comes a day after police shot and killed 22-year-old Moroccon-born Younes Abouyaaquob, suspected of driving a white Fiat van into crowds along Barcelona's famous Las Ramblas boulevard on Thursday.
Both attacks were claimed by the Islamic State group.
Oukabir was arrested after reporting that his documents had been stolen to police in the northeastern town of Ripoll, where he lived.
Speaking anonymously in line with court rules, the court official said Chemlal answered questions, but gave no details of what the suspect said in court.
Around 1 a.m. Friday, a sedan carrying five men ran into a group of people near the boardwalk in Cambrils, striking pedestrians and police, officials said.
Islamic State claimed responsibility for the Barcelona attack along with another vehicle attack Friday in which a auto crashed into people in the resort town of Cambrils, Spain, and the attackers then got out and tried to stab people.
A further 120 people were injured in the two attacks.
Abouyaaqoub's brother and friends made up the rest of the 12-man extremist cell.
Chemlal, dressed in hospital pyjamas and with his right hand bandaged, was brought in after a doctor said he was fit for interrogation, a court spokesman told AFP.
Also in court was Mohammed Aalla, the alleged owner of the Audi A3 used in the Cambrils attack.
While Spanish police say the cell has been dismantled, investigators are trying to determine if it had logistical or other forms of support from other individuals.
But the judge ruled the evidence was "not solid enough" to keep holding Aalla, who was freed on condition he appear in court weekly, relinquish his passport and not leave Spain.
Residents said Es Satty, who was in his mid-40s and had been convicted for drug trafficking in Spain, had left more than 15 years ago and had not recently returned.
This story has been corrected to show 13 were killed in Barcelona attack, instead of 14, and to correct the spelling of suspect's surname to Chemlal.