Catalan firefighters unfold a large banner with a ballot box and reading "Love Democracy" in front of the Museum of History of Catalonia on Sept. 28, 2017 in Barcelona. (AFP/LLUIS GENE)

MADRID, Sept. 28 (Xinhua) -- Barcelona police forces on Thursday morning raided a series of municipal warehouses housing ballot boxes which had been used in previous elections in the Catalan region.

The operation was to "place electoral material in custody" on the orders of the Catalan Prosecutor's office so that it could not be used in the Catalan independence referendum scheduled to be held on Oct. 1, which the Spanish Constitutional Court has ruled illegal.

The order to seize the ballot boxes was given by the Prosecutor on Wednesday night. The Prosecutor's office considers the ballot boxes to be "property of the State Administration, given to local authorities for the correct development of the electoral process".

This action came after the Catalan High Court on Wednesday ordered that public buildings which could be used as polling stations be taken over Catalan regional police to ensure they are not used on Sunday. Schools and other public buildings will also be closed and presumably sealed by local police.

Meanwhile Catalan regional leader, Carles Puigdemont, on Wednesday presented a telephone application showing where Catalans will be able to vote in the region on Oct. 1.

Ada Colou, the Mayor of Barcelona, has sent a letter to the mayors of 27 European cities, asking them to support "Barcelona's petition for the European Union to implicate itself in the Catalonia/Spain crisis".