The terror warning was highlighted by several Spanish papers today who said they had seen an internal alert sent to regional Mossos d’Esquadra officers. The revelation surfaced after the US state department tweeted: “Spain. Exercise heightened caution around areas of vehicle movement including buses in the Las Ramblas area of Barcelona during Christmas and New Year. Respected Catalan daily El Periodico said it had been told by police sources an internal alert had warned officers a man born in the Moroccan city of Casablanca could try to mow down pedestrians using a coach or similar vehicle.

Spanish daily El Pais published the initials of the man police are said to be hunting for – B.L. – and described him as a 30-year-old who had a bus licence.

It said: “The Mossos are carrying out checks on minibuses and coaches in the centre of Barcelona, as well as reinforcing security elsewhere, to try to track down the possible suspect.

A Mossos spokesman admitted this morning the force was considering issuing a statement during the day following the publication of the information.

He said: “The terror alert remains on level four out of a possible level five.

“Any warning that reaches us is analysed.”