Police clashed with Catalan separatists in Barcelona on Saturday as tensions increase before the anniversary of the Spanish region’s illegal referendum on secession which ended in violent raids by security forces.

Separatists threw and sprayed coloured powder at the local police, filling the air with a thick cloud and covering anti-riot shields, police vans and the pavement on a central boulevard in a panoply of bright colours.

Some protesters also threw projectiles and engaged with the police line, which used baton strikes to keep them back.

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Catalan police officers clash with pro- independence demonstrators in Barcelona (Emilio Morenatti/AP)

The clashes erupted after local Catalan police intervened to form a barrier when a separatist threw purple paint on a man who was part of another march of people in support of Spanish police demanding a pay raise.

Officers used batons to push back the oncoming separatists and keep apart the opposing groups.

“I make a call for calm. This city has always defended that everyone can exercise their rights to free speech,” Barcelona Mayor Ada Colau told Catalunya Radio.

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Catalan police cordon off a street to separate pro-independence demonstrators from supporters of National Police and Guardia Civil in Barcelona (Emilio Morenatti/AP)

More separatists filled a central square in Barcelona, with many having spent the night there, to force the regional government to alter the route of the march by the Spanish police supporters. Those who backed the Spanish police instead marched to another square in the city centre.

The march was organised by the police association Jusapol, which wants Spain’s two nationwide police forces, the national police and Civil Guard, to be paid as much as Catalonia’s regional police.

Jusapol holds marches in cities across Spain, but Saturday’s march in Barcelona comes two days before Catalonia’s separatists plan to remember last year’s referendum on secession that the regional government held despite its prohibition by the nation’s top court.

That October 1 referendum was marred when national police and Civil Guard officers clashed with voters, injuring hundreds.

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Catalan police officers try to stop pro-independence protesters on their way to meet demonstrations by member and supporters of the National Police and Guardia Civil in Barcelona (Emilio Morenatti/AP)

Jusapol spokesman Antonio Vazquez told Catalan television TV3 that while the march’s goal was to demand better salaries, they also wanted to support the national police and Civil Guard officers who had been ordered to dismantle last year’s referendum.

“The national police and Civil Guard agents who acted last year were doing their duty and now they are under pressure and we have to support them,” he said.

Last year’s police operation which failed to stop the referendum has become a rallying call for Catalonia’s separatists, who argue that is evidence of Spain’s mistreatment of the wealthy region that enjoys an ample degree of self-rule.

Pro-secession politician Vidal Aragones, of the extreme left CUP party, called the police march an “insult to the Catalan people”.

“It is not acceptable,” he said. “They have come here to remember the violence that they employed.”

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Catalan police officers clash with pro-independence demonstrators (Emilio Morenatti/AP)

Two weeks ago police had to intervene to keep apart two separate rallies by Catalan separatists and Spanish unionists in Barcelona, the region’s capital.

Catalonia’s separatist-led government is asking Spain’s central authorities to authorise a binding vote on secession.

Polls and recent elections show that the region’s 7.5 million residents are roughly equally divided by the secession question.