One of the five terrorists shot dead by officers in Cambrils may have been the driver of the van that killed 13 people in Barcelona, Spanish police say.
The driver, believed to be Moussa Oukabir, fled on foot after running down pedestrians on Las Ramblas.
Police launched a massive manhunt for him, but have since said he could have been killed by police during a second attack around eight hours later in the seaside town Cambrils.
"We are looking for Moussa Oukabir, but for the moment we don't know whether he was the driver of the van," police announced.
In the Cambrils attack, terrorists drove into people, killing one woman and injuring six more.
A shoot-out ensued during which police killed the five attackers - with one police officer killing four of the suspects.
Moussa is the younger brother of Driss Oukabir, whose ID was used to rent the van and whose photo police released in the aftermath of the attack.
Driss Oukabir is a Moroccan national who was from Marseille. A Facebook account says he lives in Ripoll, Catalonia, about 50 miles north of Barcelona.
He claims his brother stole his ID and reportedly handed himself in to the police station at Ripoll after he saw his photo in the media.
He said he was in Ripoll at the time of the attack.
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President of the Catalan region Carles Puigdemont told local radio there is at least one "terrorist still out there" and that "we don't have information regarding the capacity to do more harm".
Former head of National Counter-Terrorism Security Office Chris Philips told Sky News: "As long as there are areas outstanding, the police will be desperate to bring them in."
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The van used in the Barcelona atrocity is said to be a Fiat that was hired from an address in Santa Perpetua Of the Mogoda, about five miles north of the city.
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Islamic State said it was responsible for the Barcelona van attack, according to the Amaq news agency, and Spain's Prime Minister described it as a "jihadist attack".
Hours after the van attack in Barcelona, one woman was killed when the attackers drove a car into people. Several people were also injured.
Catalan authorities say the attacks are linked.