BARCELONA, Spain, Aug 20 (Reuters) - Spanish police searched on Sunday for the man behind the wheel in the Barcelona van attack that killed 13 people, amid growing signs members of the militant group had connections elsewhere in Europe.
Police said security operations were under way in Catalonia and on the French border as they searched Moroccan-born Younes Abouyaaqoub, 22, the only one of 12 suspects still at large who they believe may have crossed into France.
Others implicated in the attack have been arrested, shot by police or killed in an explosion at a house in Catalonia a day before Thursday's van attack on Las Ramblas, Barcelona's most famous boulevard.
"We don't have any specific information on this but it cannot be ruled out," Catalan police chief Josep Lluis Trapero told a news conference in Barcelona when asked if Abouyaaqoub could have crossed into France.
Spanish media say authorities believe Abouyaaqoub drove the van through crowds of tourists and locals walking along Las Ramblas, leaving a trail of dead and 120 injured. Trapero said he could not confirm who was behind the wheel.
Hours after the Barcelona attack, police shot dead five men wearing fake explosive belts in the resort of Cambrils, further down the coast, after they rammed holidaymakers with a car and stabbed others, killing one woman.
A seven-year-old British-Australian boy, Julian Cadman, was confirmed on Sunday as one of 13 killed in the Barcelona attack.
Family members told Reuters on Sunday that Abouyaaqoub had began showing more religiously conservative behavior within the past year, and refused to shake hands with women during a visit to his birthplace in Morocco in March.
They expressed shock and anger after discovering the alleged involvement in the Barcelona attack of Abouyaaqoub, his brother and two cousins, all originally from the small Moroccan town of Mrirt.
Hannou Ghanimi, Abouyaaqoub's mother, told reporters in Catalonia on Saturday she wanted her son to give himself up to police, saying she would rather see him in prison than end up dead.
Evidence emerged on Sunday that alleged members of the Catalan cell traveled to other European countries.
Hans Bonte, mayor of the Belgian town of Vilvoorde, near Brussels, told VRT television that Abdelbaki Es Satty - an imam suspected of being part of the group - was in Belgium last year looking for work.
Belgium has suffered a number of Islamist attacks and Vilvoorde has been a center of Islamic radicalism.
"We know for sure that he spent time here between January 2016 and March 2016, in Diegem, Vilvoorde and Brussels. Our local police services screened him intensely," Bonte said.
"It did not appear that on a federal level ... there was any worrying information," he added.
The Audi used in the Cambrils attack was caught speeding on camera about a week earlier in Paris, Le Parisien newspaper reported on Sunday. Spanish media say the Audi belonged to Mohammed Aalla, who was arrested after the Barcelona attack.
A Swiss newspaper, Tages-Anzeiger, reported that authorities there were investigating a visit made to Zurich last December by at least one of the Barcelona suspects.
Four people have been arrested so far in connection with the attacks - three Moroccans and a citizen of Spain's North African enclave of Melilla.
Islamic State said the perpetrators had been responding to its call to target countries involved in a U.S.-led coalition against the Sunni militant group.
Police believe the group opted to launch attacks using vehicles when their base in Alcanar, southwest of Barcelona, was destroyed in an explosion on Wednesday.
Police believe that foiled the cell's plans to carry out one or more large-scale bombings in Barcelona. More than 100 butane gas cylinders were found in the remains of the Alcanar house.
Earlier on Sunday Spain's King Felipe and Queen Letizia, Prime Minister Mariano Rajoy and Portuguese Prime Minister Antonio Costa joined Catalan leaders for a memorial service to the victims.
The city's famous football club, Barcelona FC, meanwhile increased security for its opening league match of the season late on Sunday.
"It shows that despite what happened the match has to go on," said Barcelona fan Fakih Hussein. "It's probably even safer than usual now with so much security," said Hussein, 47, who had come with his teenage son.
(Additional reporting by Sarah White, Julien Toyer, Adrian Croft, Rodrigo de Miguel, Alba Asenjo, Julia Fioretti and Robert-Jan Bartunek in Brussels, John Irish in Paris and John Miller in Zurich; Writing by Adrian Croft; Editing by Julien Toyer and Jon Boyle)