Three men go on trial over ISIS terrorist attacks in Barcelona that killed 16

Atrocity also injured 140 people after vehicles rammed into pedestrians

Mohamed Houli Chemial (L), Driss Oukabir (C) and Said Ben Iazza, the three accused of helping the perpetrators of 2017 terror attacks in Barcelona, sitting in the National Court in San Fernando de Henares near Madrid. AFP / POOL / FERNANDO VILLARShow less

Three men are on trial in Spain for helping the perpetrators of a double ISIS attack in Barcelona and a nearby seaside town that killed 16 people.

Terrorists drove vehicles into pedestrians, mainly foreign tourists, in the 2017 attacks in which 140 people were injured.

The atrocities took place on August 17 and 18 in Barcelona and Cambrils, a resort 100 kilometres to the south.

On Tuesday, Driss Oukabir, Mohamed Houli Chemlal and Said Ben Iazza, went on trial accused of being part of the terrorist cell that helped to plot and prepare the attacks.

The six people who carried out the attacks were later shot and killed by police.

In the first attack one of the terrorists plowed a van into a section of Barcelona’s crowded Las Ramblas boulevard, killing 14 people, including two children aged three and seven, and injuring many others.

The driver then went on the run, killing another person, but was shot dead by police several days later.

Five of the driver's accomplices staged a second attack in Cambrils, ramming pedestrians and stabbing a woman, who died of her injuries.

The attackers were carrying knives and wearing fake suicide vests.

On Tuesday, the court was shown a video of members of the cell, including one of the accused – Mr Chemlal – preparing explosives while they laughed and joked and threatened to carry out terrorist attacks.

Mr Chemlal told authorities after his arrest that he had been told what to say during the video and that he did not agree with what they did.

He declined to take prosecutors' questions on Tuesday but told the court he regretted the attacks.

Two members of the cell, including an imam believed to have been the ring leader, died in an explosion at a country house where they were preparing explosives hours before the vehicle attacks. Mr Chemlal was also injured in the blast.

The 23-year-old had told investigators the group had been planning attacks "on an even greater scale", with Barcelona's Sagrada Familia basilica, the city's Camp Nou football stadium and the Eiffel Tower in Paris among the possible targets.

But the accidental explosion in Alcanar, a coastal town between Barcelona and Valencia, pushed them to carry out the two attacks sooner.

The blast killed Abdelbaki Es Satty, 44, an imam who was allegedly responsible for radicalising the trio.

Taking the stand, an unidentified investigator said evidence was found that August 20 would be the date they "very likely planned to carry out a terrorist attack" with vans, explosive vests and grenades.

The likely target would be Barcelona's football ground Camp Nou during a match with a focus on the exits, he said.

However, on August 15, the accidental explosion changed their plans.

The investigator told the court the imam killed was their "spiritual leader" who would send orders to his most-trusted inner circle which included three of the attackers.

Mr Chemlal was in the second circle of trust, Mr Oukabir in the third, meaning he "took part but not in such a direct way" as the others," the witness added.

The security official said cell members were linked by close friendship and family ties and did not interact with outsiders.

"They had all known each other since they were small, making the group practically impenetrable," the investigator testified.

"The secrecy between them was extraordinary."

Antonio Guerrero, a lawyer for the AVT terror victims' association said all three should be tried for "terrorist murder".

"In our opinion, they were part of the cell," he said.

Lawyer Jaume Alonso-Cuevas said there were "too many unanswered questions".

"We want the state to be accountable for not regulating the sale of explosives purchased by the cell to prepare for attacks."

The trial is taking place at Spain's National Court in San Fernando de Henares, near Madrid, and is expected to run until December 16.

Prosecutors are seeking a 41-year prison term for Mr Chemlal, who is charged with belonging to an ISIS terrorist group, the manufacture and possession of explosives and conspiracy to wreak havoc.

Mr Oukabir, 31, whose brother was one of the attackers, rented the van used in the Barcelona attack and is facing the same charges as Chemlal. Prosecutors want him jailed for 36 years.

On Tuesday, he denied being part of a terror cell, insisting he "wasn't religious".

He said his brother and 22-year-old Younes Abouyaaqoub, the Barcelona driver, had asked if he would hire a van as a favour "for moving house, because they weren't old enough to rent one".

Mr Iazza, 27, has admitted lending his ID card and vehicle to two business customers who said they were going to buy cleaning products.

He denied knowing they wanted to fabricate explosives and, like Mr Oukabir, insisted he did not know Es Satty.

Prosecutors are seeking an eight-year sentence for Mr Iazza.

The 16 victims of the attacks came from several countries, including Spain, Belgium, Germany, Italy and Portugal.