MADRID (AP) — Security is high in Barcelona following a U.S. warning of the risk of a terror attack during the Christmas and New Year's holidays.

The security alert, posted online and sent to U.S. citizens in Spain's second-largest city, recommends exercising "heightened caution" around buses and public transport in the Las Ramblas area. Barcelona's downtown boulevard, beloved by tourists and residents, was targeted last year during an attack claimed by Islamic State militants that killed 14 people.

The regional Mossos d'Esquadra police declined to comment Monday directly on the alleged threat, saying only that security had been heightened "as part of a previously arranged anti-terrorist vigilance for the Christmas period."

Spain's Interior Ministry said the level of anti-terror alert in the country remained at the second-highest level, unchanged since 2015.