One of the men accused of plotting the Barcelona terror attack admitted during a court hearing on Tuesday that his group was planning a much bigger attack.

The 21-year-old man from the Spanish exclave Melilla in North Africa was attempting to manufacture a bomb when his creation accidentally detonated last week, destroying a warehouse, prosecutors alleged.

He was allegedly part of a 12-member terror cell that went on to kill 15 people and injure 120 others in the August 17 Barcelona attack attack on Las Ramblas in Catalonia. 

Only four alleged members of the cell are still alive, with the remaining eight either dying in the warehouse explosion or being shot dead by police in Barcelona.

The four remaining members were facing the National Court in Madrid on Tuesday. The court is closed to media but people inside the trial have been briefing news agencies.

One of the suspects was released, two of the suspects were sent to jail pending a full trial and one of the suspects was to remain in police custody for further questioning, the judge ruled late Tuesday. The man released was the registered owner of the Audi A3 that was used in the Cambrils attack. He told the court that the car was in fact his brother's even though it was registered in his name. The court ruled there was not enough evidence to detain him.

Two of the men were charged with membership of a terrorist organization, murder and possession of explosives.

Read more: Catalonia's Islamic extremism problem

Several Spanish outlets reported the man told the court he was planning to attack one of Barcelona's monuments. Authorities did not confirm speculation that they were targeting the Sagrada Familia cathedral. 

Suspect thought the van was to move house

One of the four suspects was arrested in the town of Alcanar, south of Barcelona, where a house exploded last Wednesday. Police now believe it was a botched bomb-making workshop and that the explosion foiled plans for a larger attack after finding dozens of gas canisters. The other three were arrested in the small town of Ripoll north of Barcelona, where most of the members of the suspected cell had lived.

Another suspects told the court that he did rent the vans used in the attack but thought they would be used to move house.  

He denied being part of the attackers' cell, telling the court that he was acting in fear when he told police that his documents were stolen by his brother. He was the second person to face court.

Most terror suspects killed

Two of the suspects accused Moroccan imam Abdelbaki Es Satty of being the ringleader of the group. They told the court that the imam planned to blow himself up as part of a bomb attack on a Barcelona monument. However, the man was killed in the warehouse explosion in Alcanar.

Satty is alleged to have radicalized the younger men, many of them groups of brothers. Five apparent cell members were shot dead by police after they rammed a car into pedestrians in the resort town of Cambrils, got out and tried to stab people wearing fake explosive belts. A Spanish woman died in the attack, which occured hours after the one in Barcelona.

On Monday, police shot dead the 22-year-old who they had identified as the driver of a van which ploughed into crowds on Barcelona's popular Las Ramblas boulevard, killing 13 people and wounding at least 100. Younes Abouyaaquob is also accused of killing the driver of a car he hijacked to make a getaway.

International links probed

Catalan police said that although all 12 suspects were either dead or in custody, they would continue to investigate whether the cell had international links. The "Islamic State" terror group was quick to claim responsibility for the attacks in Barcelona and Cambrils, but often claims attacks it had no concrete role in. Materials for making the group's preferred explosive, TATP, were found in the Alcanar house.

Read more: 'Resilient Barcelona' stands up against fear

French Interior Minister Gerard Collomb on Tuesday confirmed media reports that the Audi used in the Cambrils attack had earlier been caught on a speed camera in the Paris area. Spanish police have also been working with Belgian authorities to investigate a visit that the imam, Es Satty, made there last year.

se, aw/rt (Reuters, AP, AFP, dpa)