Security in Barcelona is reportedly on high alert following a warning from the U.S. of the risk of a terror attack over the holidays.

The State Department in a tweet urged "heightened caution around areas of vehicle movement" in Barcelona's Las Ramblas area during Christmas and New Year's.

"#Spain: Exercise heightened caution around areas of vehicle movement, including buses, in the Las Ramblas area of Barcelona during Christmas and New Year’s. Terrorists may attack with little or no warning, targeting tourist locations, transportation hubs, and other public areas," the warning reads.

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Police in Spain declined to comment on any specific threats Monday, according to The Associated Press, but said that security has been increased “as part of a previously arranged anti-terrorist vigilance for the Christmas period.”

The Spanish Interior Ministry told ABC News the level of anti-terror alert holds at the country’s second-highest level, where it has been since 2015.

In April of 2017, Barcelona, Spain's second-largest city, saw a terror attack that killed 14 people when a man drove a van into pedestrians on La Ramba, a central street popular with tourists. ISIS took credit for the incident.