: “We cannot rule out more attacks. There have been assaults in the past and there will be more in the future.”
The group says that mass tourism is spoiling Spain, and pushing locals out by driving up rental prices.
Even graffiti in the city has turned menacing with one slogan, featuring a black silhouette with a red target on its head, reads: "Why call it tourist season if we can't shoot them?"
There is concerns that the violence could spread.
Spanish Prime Minister Mariano Rajoy intervened this week after some anti-tourist anger turned physical in Mallorca.
A video emerged of masked Arran activists setting off flares outside a restaurant full of tourists on the island of Palma de Majorca. They then entered the restaurant and threw confetti at frightened diners.
Slogans demanding tourists go home have been written over the Old Town walls in Palma Credit: Reuters This graffiti claims tourists are the terrorists Credit: Reuters Youth activists are also planning a protest in San Sebastian, northern Spain, later this month.
Rajoy described the activists as "extremists going against common sense".
Tourism makes up 12 percent of Spain's economy, and visitors to the country jumped 12 percent in the first half of 2017 to 36.4 million.
The backlash has sparked concerns for one of the region's biggest economic drivers and prompted authorities to act.
Rome is considering limiting visitor numbers to parts of the eternal city, such as the Trevi fountain. Dubrovnik plans to limit cruise ships.
Parts of cities are being overcrowded by tourists pushing the locals out Credit: Getty - Contributor Barcelona is planning a new tourism tax.
In Venice last month, residents marched through a throng of visitor to protest against uncontrolled tourism. They did so behind a banner: "My future is Venice".
Of the protests in Spain, a spokesman for the Foreign Office said: “We are aware and monitoring the situation. We are also in contact with the local authorities. There is no specific update to our travel guidance but we keep it under constant review.”
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