Spanish police have raided the flat of a man they think may by the ringleader of the group behind the terror attacks.
It is thought the imam, who has not been seen since Tuesday, may have radicalised the young men.
The terror cell responsible for attacks in Barcelona and Cambrils has been dismantled, but a manhunt for one suspect is continuing, Spanish authorities have said.
Spanish interior minister Juan Ignacio Zoido said police have broken the "terrorist cell from Barcelona" - after he said five members were shot dead, four were in custody and as many as two were killed in an explosion.
He said no new attacks were imminent, that they will be maintaining the country's terrorist threat alert at level four, and security at popular events and tourist sites around the country will be reinforced.
Catalan Police spokesman Albert Oliva confirmed a search is underway for any remaining members of the Islamic extremist cell, with the search focused on Younes Abouyaaqoub, a 22-year-old Moroccan.
Abouyaaqoub has been named in Spanish media as the suspected driver of the van which was used in the massacre on Las Ramblas that left 13 dead and nearly 130 injured.
Fears were continuing to grow over the fate of seven-year-old Julian Cadman, understood to be a dual British-Australian national, who became separated from his mother during the Barcelona attack.
Speaking after the family made an initial plea for help to find the missing boy, British Prime Minister Theresa May said a child with dual British nationality was believed to be among those unaccounted for.
Julian's father and grandmother are believed to have arrived in Spain on Saturday after travelling from Australia.
Some 34 nationalities were among those wounded in the attacks in Las Ramblas and in Cambrils, which lies around 70 miles to the south west.
Catalan authorities said they have identified eight victims of the attack in Barcelona as an Italian, two Portuguese, three Spanish, one Spanish-Argentine and an American.
The victim of the second assault in Cambrils has been identified as a Spanish woman.
Family members or government officials have said another two Italians, a Belgian and a Canadian are also amongst the dead following the attack in Barcelona.
In the wake of the twin attacks Spain's King Felipe VI and Queen Letizia visited the victims of the atrocity and spoke to medical staff at Barcelona's Hospital del Mar.
The royal couple then laid a wreath on Las Ramblas promenade, among a growing number of candles and floral tributes.
On Friday it emerged another suspect, Moussa Oukabir, who is thought to have rented the van, was among five men shot dead as they launched a second attack in the coastal town of Cambrils.
The teenager, said to be 17 or 18 years old, is suspected of using his brother's documents to hire the vehicle that ploughed through pedestrians in the tourist hotspot on Thursday evening.
He reportedly died along with Said Aallaa, 19, and Mohamed Hychami, 24, who were part of a group that mounted a similar attack in Cambrils that left one woman dead and six people injured.
The identities of the other two dead attackers are yet to be confirmed by police.
Four men, aged 21, 27, 28 and 34, who were arrested in connection with the attack remain in custody.
Three are Moroccan and one Spanish, and police said none of them was previously known to the security services for terror-related reasons.
Moussa Oukabir's older brother, Driss Oukabir, is reported to be one of those detained.
Authorities said 53 people injured in the attacks were still in hospital on Saturday, with 13 in a critical condition and 22 in a serious condition.
Police said the terrorists behind the rampage were preparing bigger attacks, with a suspected gas explosion on Wednesday at a house in Alcanar believed to have robbed the killers of materials to use in larger-scale operations.
Catalan regional police official Josep Lluis Trapero told reporters on Friday: "We think they were preparing at least one or more attacks in Barcelona.
"The explosion in Alcanar at least avoided some of the material they were counting on to carry out even bigger attacks than the ones that happened.
"Because of that the attack in Barcelona and the one in Cambrils were carried out in a bit more rudimentary way than the one they had initially planned."
On Saturday police carried out controlled explosions in Alcanar, and also raided the house of an imam believed to be the radicalising force behind the cell, the Associated Press reported.
Police are also looking for a white Kangoo vehicle which is believed to have been rented by the suspects and could have crossed the border into France, according to French media.
The attacks in Barcelona and Cambrils took place around eight hours apart on Thursday afternoon and in the early hours of Friday.
In an echo of the London Bridge attack in June, Catalonia regional president Carles Puigdemont said the five terrorists in the Cambrils car were wearing fake suicide belts when they were stopped.
Police said that an axe and knives were also found in the vehicle, with one of the latter used to wound one person in the face before the terrorists were gunned down.