A woman places a candle on a placard, reading in Spanish and Catalan "Catalonia, place of peace", in the area where a van crashed into pedestrians at Las Ramblas street in Barcelona, Spain August 18, 2017. REUTERS/Sergio Perez

WASHINGTON (Reuters) - U.S. President Donald Trump said the United States was prepared for any possible “trouble” and its borders were secure, as authorities in Spain grappled with an attempted attack near Barcelona one day after another attack left more than a dozen dead.

“Homeland Security and law enforcement are on alert & closely watching for any sign of trouble. Our borders are far tougher than ever before!” Trump wrote in a post on Twitter on Friday.