Five terrorists wearing fake suicide belts have been killed by police following the Barcelona attack, while three suspects are in custody.
Britons in the Catalonia capital and in the seaside town of Cambrils - the scene of a second attack in the early hours of Friday, around 70 miles (113km) west along the coast from Barcelona - described running for their lives after a suspected Islamist terrorist drove a van into crowds through the tourist hot spot of Las Ramblas.
At least 13 people died and more than 100 people were injured in the massacre, the deadliest attack in Spain since the 2004 Madrid train bombs in which more than 190 people were killed.
Catalonia president Carles Puigdemont said the five terrorists shot by police in Cambrils - where a car ploughed into pedestrians - were wearing fake suicide belts when they were stopped, and linked them to the earlier Barcelona attack.
There were also reports that investigators believe the eight-strong terror cell may have been planning an attack using gas canisters.
It came as it was confirmed that an Irish family was caught up in the Barcelona attack.
The mother and father were originally from the Philippines and are naturalised Irish citizens, while their two children were born in Ireland.
Their injuries are understood to be non life-threatening.
Witnesses to the attack said the van hurtled through crowds in Las Ramblas without slowing down, sending scores of people scattering, with many taking shelter in nearby shops.
On Thursday, lawyer and University of Glasgow rector Aamer Anwar described the horror of the scene with people "screaming and running and jumping into shops".
But on Friday he returned to the bustling street, telling the Press Association that "life seems to be going back very quickly to normality".
Prime Minister Theresa May said she was "sickened" by the incident, while the Foreign Office said it was still trying to determine if there were British victims.
Seven people, including a police officer, were injured in the incident in Cambrils.
Bystanders ran for their lives as gunfire broke out close to the coastal town's beachfront promenade, while residents of the popular tourist spot were ordered to take cover indoors as bullets tore through the air.
Fitzroy Davies, from Wolverhampton, was caught up in the second attack and described how police shot dead one of the attackers.
He told the BBC he was in Spain for a judo camp and was in a meeting with the coaches when the incident unfolded.
"These girls ran into the bar off the street and then people were running up the road," he said.
"One of our guys stood up, looked and just said 'run', so we all ran.
"This guy came running up the road and was shouting something.
"I didn't know what it was, so we said call the police.
"Within 30 seconds the police was already there, jumped out of the car, started shouting at the guy; the guy was then saying something else again.
"And then they - 'pop, pop' - did a couple of shots and he fell down.
"He stood back up and then he stepped over the fence and he started, he was taunting, smiling and he carried on walking to the police, and then they gave it to him again, a couple more shots and then he fell to the ground."
Mr Davies told Sky News one of his associates at the camp was "slightly injured" after a bullet "ricocheted", and suggested the suspect had been "laughing" at police before he was taken down.
Several controlled blasts were carried out in the area in the wake of the attacks.
Mossos, Catalonia's police force, said four of the attackers were shot dead at the scene and later confirmed a fifth had died of his injuries.
Of the six civilians caught up in the Cambrils attack, two were said to be in a serious condition.
Reports in Spain suggested detectives were investigating a possible cell of eight people thought to have been involved in planning the attacks.
Two suspects, a Spanish national from Melilla and a Moroccan, were taken into custody in the wake of the attack. A third was arrested later.
It has not been confirmed if the Barcelona van driver, who fled the carnage, is among them.
Mr Puigdemont told local radio there was at least one "terrorist still out there", but that "we don't have information regarding the capacity to do more harm".
It was not clear whether the terrorist he referred to was the van driver.