Tourists have been put on high alert after police in Barcelona were warned of a possible Christmas Day terror attack 'by a Moroccan man with a bus driver's licence'.

Officers have been told a 30-year-old Casablanca-born terrorist with the initials B.L. may try to commit a spectacular massacre in the Catalan capital using a coach or similar type of vehicle.

The revelation surfaced after the US state department warned tourists to exercise extreme caution along the city's famous Las Ramblas - the site of a deadly jihadist vehicle attack in August 2017.

A tweet said: 'Spain. Exercise heightened caution around areas of vehicle movement including buses in the Las Ramblas area of Barcelona during Christmas and New Year.

Tourists have been put on high alert after police in Barcelona were warned a Moroccan man could carry out a terror attack in the city on Christmas Day. The revelation surfaced after the US state department warned tourists to exercise extreme caution along the city's famous Las Ramblas - the site of a deadly jihadist vehicle attack in August 2017 (pictured)

'Terrorists may attack with little or no warning, targeting tourist locations, transportation hubs, and other public areas.'

The latest terror warning was highlighted by several Spanish papers today who said they had seen an internal alert sent to regional Mossos d'Esquadra officers.

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.

It said the alert had mentioned Christmas Day as the date for the possible attack and said the regional Mossos d'Esquadra had given it 'medium' credibility.

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/yesterday morning (MON) the force was considering issuing a statement during the day following the publication of the information.

The US state department has urged tourists to 'exercise heightened caution around areas of vehicle movement including buses in the Las Ramblas area of Barcelona during Christmas and New Year'

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

'Any warning that reaches us is analysed.'

Moroccan Younes Abouyaaqoub, 22, used a rented van to mow down and kill 15 people including British-born Julian Cadman, seven, in Barcelona's famous Las Ramblas on August 17 last year.

More than 130 people were injured.

Police shot dead Younes in vineyards in Subirats an hour's drive west of Barcelona after he went on the run following the Barcelona massacre. He was later buried in an unmarked grave in a funeral held in secret in his homeland.

City hall chiefs installed metal bollards after the attack to stop vehicle access.

Last Friday police in Barcelona arrested a 33-year-old Moroccan described as a 'dangerous ISIS terrorist' who had managed to reach Spain after fighting in Syria.