Auxiliary Bishop Sebastia Taltavull called for peace and coexistence and prayed for a quick recovery for the more than 100 people injured on Thursday when a van plowed into pedestrians on Barcelona's popular Las Ramblas promenade, killing 13.
According to Catalan police, Abouyaaqoub is risky and possibly armed.
The police fatally shot five men, including Moussa Oukabir, in Cambrils, 60 miles southwest of Barcelona, during a second attack hours after the first.
The 35-year-old global aid worker, Pau Perez, who was found stabbed to death in his vehicle in the University area of Barcelona, has been confirmed as the 15th victim.
The Catalan regional government said on Monday that European police forces were searching for Abouyaaqoub, fearing he may have crossed the border into France. Police earlier said they had shot a man wearing an explosive belt but did not immediately identify him as Abouyaaqoub.
Police believe he later killed a man during a carjacking during his escape.
Police suspect the terrorist cell was also behind the explosion at a house in the town of Alcanar some 200 kilometers from Barcelona on August 16.
Police say they are investigating the possibility that, some 90 minutes later, the suspect stabbed and killed a Spanish man and stole his auto. The suspects were gunned down by police as they left the vehicle, with one reportedly brandishing a knife.
The Spanish bomb squad sent a robot to inspect his body but concluded the explosives were not real.
The van attack in Barcelona killed 13 of the 15 victims in a string of linked terror attacks on Thursday. "We don't know where he is", said police chief official, Josep Luis Trapero in a press conference.
Both President Donald Trump and the Department of Homeland Security committed to helping Spain in the wake of the attack.
He denied being part of the attackers' cell, telling the court that he was acting in fear when he told police that his documents were stolen by his brother.