Meanwhile, hundreds more pro-independence supporters protested outside a courthouse in the north-eastern Catalan town of Hospitalet de Llobregat to demand the release of the arrested officials.
On November 9, 2014, about 80 percent of the Catalans who took part in a non-binding referendum on the region's status as part of Spain voted in favor of Catalonia becoming an independent state.
A Catalan regional judiciary body statement said the six declined to testify Friday when brought before the judge. They include Josep Maria Jove, the secretary general of economic affairs for the region and No. 2 to the region's vice president, Oriol Junqueras.
Civil Guard police this week arrested around a dozen regional government officials and seized about 10 million ballot papers.
A ministry statement says the agents will provide backing for the Catalan regional police who are also under orders to prevent the October 1 referendum from taking place.
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'Greater harm'Spanish Prime Minister Mariano Rajoy, whose opposition to the referendum has the support of the main opposition Socialist party, has warned Catalan leaders of "greater harm" if they don't call off the referendum bid. Police said up to 40,000 people gathered outside the devolved government's economy ministry in the city, which was searched. They occupied a central cloister near the offices of the dean and other university officials. It didn't say how many extra police would be sent.
Some are billeted in three ferries rented by the Spanish government and moored in the harbours of Barcelona and Tarragona because of both a shortage of temporary housing and to avoid clashes between protesters and police forces.
Catalans have launched a hate campaign against Spaniards who oppose the controversial independence referendum, sending photographs of nooses to several councillors and, in one case, calling for a woman to be gang-raped.
The constitutional court says the vote is illegal but the region's vice-president said it would go ahead if possible.