In a tweet in English, Mossos d'Esquadra, the Catalan police force, said they confirmed that Abouyaaqoub, who they described as the "author of the terrorist attack in #barcelona" had been "shot down" in Subirats, a town just west of Barcelona on Spain's Mediterranean resort coast.
"He was the only person who was still at large and had been a prime person of suspect", Al Jazeera's Sonia Gallego, reporting from Barcelona, said.
Local media suspect Abouyaaqoub was behind the wheel of the white van which plowed through crowds on the tourist-heavy boulevard, leaving a trail of dead and 120 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. Abouyaaqoub ran from the scene of the terror attack by foot, stabbed a driver to death, stole his auto and crashed into a police blockade while attempting to flee. His older brother Driss is among the four arrested.
He had been the only at-large member of the 12-strong terror cell behind the attacks in Barcelona on Thursday and in the seaside town of Cambrils early on Friday.
Authorities in Spain have confirmed that Younes Abouyaaqoub is the final member of the Islamic extremist cell at large after the attacks in Barcelona and a nearby town.
Hours later, he's believed to have helped carry out a linked attack Cambrils, south of Barcelona.
Julian Cadman became separated from his mother
Abouyaaqoub was suspected of driving the van that ploughed down the Las Ramblas promenade.
An global manhunt is continuing for the 22-year-old Moroccan who is suspected of driving the van used in the Barcelona terror attack.
Spanish authorities were also officially notifying European police Monday of the identity of the suspect to enable the launch of a Europe-wide manhunt.
Police had fired at the auto when it forced the checkpoint, injuring an officer, and initially thought the man they found in the vehicle had been killed by the gunfire. He stabbed the vehicle's driver, Pau Perez, to death and barreled through a checkpoint, authorities said.
Several of those suspected of involvement in the attacks are thought to come from Ripoll, an inland town of 11,000 people about 60 miles (100km) north-west of Barcelona. Human remains were found in the rubble left by the blast, which police believe may have been caused by mishandling butane canisters that were meant to be used in an attack.
Police used a robot Monday to remove the suspected explosives belt.
The attack in Barcelona, capital of the Spanish region of Catalonia, was therefore "more rudimentary than they originally planned", Trapero said.
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