Barcelona, September 20 (RHC)-- Spanish police on Wednesday seized "nearly 10 million ballot papers" in Catalonia which were to be used for an independence referendum banned by Madrid, the interior ministry said.

A source close to the case who requested anonymity added that the ballots were confiscated in Bigues, about 45 kilometers (28 miles) north of Barcelona.

The seizure comes as thousands took to the streets in Barcelona on Wednesday over the detention of 13 Catalan government officials as the wealthy northeastern region presses ahead with preparations for the October 1st vote.

Catalonia's separatist leaders want the region's 7.5 million inhabitants -- who are deeply divided over the issue -- to be able to answer the question: "Do you want Catalonia to be an independent state in the form of a republic?"

But the country's Constitutional Court has deemed such a referendum unconstitutional.

The constitution states that the unity of the Spanish nation is "unbreakable" and that only the central government has the power to call a referendum on an issue. Catalan separatists have retorted that they have a democratic right to decide on their future.

Operations were also underway Wednesday at several offices of the Catalan executive, including the presidency and the departments of economic and foreign affairs.

Over the past few days, police have ramped up their seizure of items that could be used in the referendum, including notifications waiting to be sent to Catalans selected to staff polling stations.

Madrid has also threatened to arrest mayors who facilitate the vote and has tightened its control over the region's finances.

Separatist parties captured 47.6 percent of the vote in a September 2015 Catalan election which was billed as a proxy vote on independence, giving them a narrow majority of 72 seats in the 135-seat Catalan parliament.

But opinion polls show that Catalonia remains divided on the question of seceding from Spain.

A survey commissioned by the regional government in July showed that 49.4 percent of Catalans were against independence while 41.1 percent were in favor.

Madrid has taken over the payment of essential services and public workers’ salaries in Catalonia to prevent the money from being spent on a banned referendum.

Catalonia’s leader accused Madrid of imposing a "de facto state of emergency" in the Spanish region, with a series of measures to prevent an illegal independence referendum taking place.

In a speech following the latest move by Madrid -- the detention of 13 regional government officials -- Carles Puigdemont also claimed the Spanish state had implemented a "de facto suspension of Catalonia's self-governance" by for instance tightening control over Catalan finances.