Regional authorities in Catalonia have denied reports that US anti-terrorism officials warned them of a planned attack in Barcelona.
However, they admitted receiving tips of possible attacks from other sources they deemed not very credible.
Catalan regional interior chief Joaquim Forn said regional police were not warned by the CIA or the National Counterterrorism Centre, adding that such warnings would be made through state channels.
The Barcelona-based El Periodico newspaper said the US sent the warning on May 25 to regional police, specifically mentioning Las Ramblas.
A van attack on August 17 on Las Ramblas killed 14 people.
One other person was stabbed to death by the Barcelona attacker as he fled.
Another attack in nearby Cambrils left one person dead.
The US embassy in the Spanish capital Madrid said it could not comment on intelligence issues.