Spain will deploy police reinforcements to Catalonia to help maintain order if an independence referendum pledged by Catalan officials but opposed by the national government goes ahead, officials said Friday.

The measure came amid rising tension between Spanish and Catalan authorities over the planned Oct. 1 ballot.

Civil Guard police this week arrested around a dozen regional government officials and seized about 10 million ballot papers. Street protests against those measures grew ugly, with demonstrators vandalizing two police cars, and a prosecutor asked Friday for Spain's National Court to consider investigating demonstrators for sedition.

Spain sends extra police, tanks to Catalonia in new bid to clamp down on planned independence referendum https://t.co/2eXUsqRZGs pic.twitter.com/lGOhWuZpbK — DAILY SABAH (@DailySabah) September 22, 2017

Authorities in the wealthy northeastern region insist the vote will take place, even though Spain's Constitutional Court has ordered it to be suspended and the Madrid-based national government insists it is illegal.

An Interior Ministry statement said the extra agents would provide backing for the Catalan regional police, who are also under orders to prevent the staging of the referendum.

The statement said the Catalan Interior Ministry had been informed. It did not say how many extra police would be sent. Three ferries docked at Barcelona's port will provide accommodation for the extra officers.

Also Friday, a Catalan regional judge ordered the release with restrictions of six people arrested Wednesday in the crackdown on referendum preparations. A statement said the six declined to testify.

They remain under investigation for disobedience, abuse of power and embezzlement in relation to the planned ballot and must appear before the court each week.

A large and noisy demonstration lasting more than 24 hours in Barcelona against the raids and arrests dispersed Friday afternoon after the officials were released.

Some 2,000 students were still staging a separate pro-referendum demonstration at one of Barcelona's main universities, however. They occupied a central cloister near the offices of the dean and other university officials. Student union representatives urged the protesters to remain over the weekend.

Catalonia represents a fifth of Spain's 1.1-trillion-euro ($1.32 trillion) economy and enjoys wide self-government. The region has about 5.5 million eligible voters. Polls consistently show the region's inhabitants favor holding a referendum but are roughly evenly divided over independence from Spain.