Far-right demonstrators performed Nazi salutes as they took to the streets of Barcelona to protest against Catalan independence on Saturday (7 October).
They broke into fascist chants as they marched through the city at a procession organised by Spanish far-right party Falange Española de las Jons, which was last in power during the dictatorship of Francisco Franco.
The extremists waved fascist flags from Franco's era, which are banned in Spain.
Tens of thousands of people protested against Catalan independence over the weekend, after Catalonia's leader Carles Puigdemont said his government would hold a secession vote from 9 October.
Some 90% of those who cast their ballot in the referendum voted 'yes', but Spain's Constitutional Court has declared the vote illegal.
Over the weekend, protesters called for Puigdemont to be imprisoned after he pledged to push for independence.
Spanish Prime Minister Mariano Rajoy has said that he will not allow Catalonia to become independent and promised in an interview with newspaper El Pais to employ any measure "allowed by law" to stop Catalan separatists.
Rajoy said an option was triggering Article 155, which allows the Spanish government to take control of regional affairs "if the regional government does not comply with the obligations of the Constitution".
"The ideal situation would be that I don't have to find drastic solutions," he told the paper. "But for that to happen there will have to be some rectifications."
The constitutional crisis in Spain, which is the fourth-biggest economy in the euro zone, has caused stocks and bonds to tumble.
Tourism and production in Catalonia fuel the Spanish economy, with the region's output totalling a fifth of Spain's GDP.