BARCELONA (Reuters) - Demonstrators calling for Catalan independence gathered in hundreds of towns across the region on Sunday following Madrid’s actions last week to try to block a referendum on self rule that it considers illegal.

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Spanish police have arrested Catalan officials who were involved in organising the Oct. 1 vote and they also seized electoral material, including ballot papers and ballot boxes. This led to several days of protests in Barcelona.

But Carles Puigdemont, the head of the Catalan regional government, has said the referendum will go ahead.

Several thousand protesters gathered in central Barcelona on Sunday chanting “We will vote!” and handing out ballot papers. The crowds began whistling and booing a police helicopter during speeches by the protest organisers, showing growing anger among the referendum supporters about the increased police presence.

Between 3,000 and 4,000 state police officers from other regions of Spain have arrived or are on their way to Catalonia.

“We feel occupied by the Spanish police,” 56-year-old interior designer Nuria Gimenez said. “We’ve been protesting for 10 years, we’re not going to stop now with one week to go. We need to keep going until the end.”

On Saturday, the state prosecutor in Catalonia told all local and national police forces they would be placed temporarily under a single chain of command and report directly to the interior ministry in Madrid.

The Catalan government initially said it would refuse the order, though the head of the Catalan regional police, known as the Mossos d’Esquadra, later said he would comply with prosecutors.

Speaking to the crowd in Barcelona, president of the Catalan Parliament Carme Forcadell said that separatists must resist “provocations” by the central government.

“They see violence in Catalonia. There has been none, nor will there be. We are a peaceful people and all we want is to exercise our rights,” Forcadell said.

Although polls show less than half of Catalonia’s 5.5 million voters want self-rule, most in the wealthy northeastern region want the chance to vote on the issue.