An international manhunt is continuing for the 22-year-old Moroccan who is suspected of driving the van used in the Barcelona terror attack.

French police have ramped up border checks in the hunt for fugitive Younes Abouyaaqoub as details emerged of the terror gang's attack planning.

Abouyaaqoub has remained at large since Thursday's massacre on Las Ramblas and later van attack in the Catalan resort of Cambrils, which killed 14 and injured more than 130.

Three other named suspects who were wanted by police have been confirmed to have been among the five attackers shot dead in Cambrils in the early hours of Friday.

They include 17-year-old Moussa Oukabir, who is thought to have rented the van.

Spanish authorities believe one of the gang rented a separate Kangoo utility vehicle that may have crossed the nearby border into France, a French security official said.

French police are stopping vehicles crossing the western Pyrenees to check drivers' IDs and the contents of their cars, mainly targeting vans, trucks and utility vehicles.

Catalan police are meanwhile carrying out controlled explosions in the town of Alcanar, where the extremist cell plotted the twin Catalan van attacks at a rented house.

The house was destroyed on Wednesday by an apparently accidental explosion.

Flowers, messages and candles left in tribute to the victims of the Barcelona attack. Credit: AP

Police believe the blast may have prevented a far more deadly attack using explosives, forcing the extremists to use more "rudimentary" vehicles instead.

Spain's interior minister Juan Ignacio Zoido declared the attackers' terror cell "totally dismantled" despite Abouyaaqoub still to be apprehended.

Authorities confirmed the country's threat level would not be raised from level 4 to its maximum level 5.

However, Mr Zoido said security would be raised for events that draw large crowds and popular tourist sites.

Muslims held signs reading 'Islam means Peace' in a demonstration at the Barcelona attack site. Credit: AP

A small group of Muslims visited the attack site on Las Ramblas and chanted "we are not terrorists" and Islam is peace" at the Canaletas Fountain at the top of the famous promenade.

Catalan's Moroccan community, in particular, has been in the spotlight after the four main suspects in the attacks claimed Moroccan roots.

Moussa Oukabir, 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.

Suspects Moussa Oukabir, Mohamed Hychami and Said Aallaa are believed to have been killed.

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 suspected jihadists 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, who has claimed his ID was used to hire the attack van without his knowledge, is understood be one of those detained.