A third suspect has been arrested in connection with the Barcelona attack, the Catalonia interior ministry said.
The suspect was reportedly arrested in the northern Catalan town of Ripoll.
Police are already holding two people in custody over the attack. But they have yet to release their identities or announce any charges.
It is thought the driver of the van, which ploughed into the busy Las Ramblas area killed at least 13 and injuring 100, is still on the run.
Hours after the Barcelona attack, police shot dead five suspected terrorists who drove into people in the Spanish coastal town of Cambrils.
Seven people, including a police officer were injured.