Thirteen people were killed when a van, believed to be rented by the Oukabir, ploughed into crowds in Las Ramblas on Thursday afternoon.
Later that night, police shot five attackers including Oukabir, who is believed to be 17, in the nearby town of Cambrils after a car rammed pedestrians, killing one woman and injuring six people.
Police have said Aallaa and Mohamed Hychami, who they had earlier put on a wanted poster with Oukabir, were also dead.
Younes Abouyaaqoub, who has been named as the fourth suspect, remains unaccounted for.
Four others have been arrested, one in Alcanar after Wednesday's explosion and three in the Catalan town of Ripoll after the Barcelona attack.
Some 34 nationalities were among almost 130 people wounded in the attacks in Barcelona's popular Las Ramblas shopping area on Thursday and in Cambrils, a seaside town 70 miles to the south west, early on Friday.
Prime Minister Theresa May said a child with dual British nationality was believed to be among those unaccounted for, after a grandfather made a desperate online plea for information about his young grandson's whereabouts following the van attack in the Catalan capital.
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