Spanish police have arrested the Catalan region's junior economy minister as part of a morning raid on several government offices in the run-up to an independence referendum, according to sources within the regional government.

Besides arresting Josep Maria Jove, police on Wednesday entered the local government offices of the economy, interior, foreign affairs, welfare, telecommunications and tax, the sources said.

Spain's Guardia Civil police on Wednesday searched several headquarters in Barcelona of Catalonia's regional government, a Catalan government spokesman said.

Al Jazeera's Karl Penhaul, reporting from Catalonia, said the police are looking for any evidence of wrongdoing, "and evidence of support by the regional government for the October 1 independence referendum, which the central government has dubbed undemocratic and illegal".

The operation comes amid mounting tensions as Catalan leaders press ahead with preparations for the independence referendum on October 1 despite Madrid's ban and a court ruling deeming it illegal.

Catalan leader accuses Spain of "totalitarian attitude" and ''unlawful" arrest of officials.

Police were searching the Catalan government's offices of economic affairs, foreign relations and the presidency, the spokesman said.

READ MORE: Spain - Is this the end of the Socialists?

The operation comes a day after police seized a trove of documents related to the October 1 referendum from the offices of private delivery company Unipost in the Catalan city of Terrassa.

Pro-separatist parties captured 47.6 percent of the vote in a September 2015 regional election in Catalonia viewed as a proxy vote on independence, giving them a narrow majority of 72 seats in the 135-seat Catalan parliament.

Control of finances

Spanish authorities on Monday took control of Catalonia's finances to prevent funds being used for the independence referendum, a move that limits the region's autonomy and puts in doubt the payment of thousands of public workers' salaries.

Earlier, on Friday, the conservative government announced it would take over the payment of essential services and public workers' salaries in Catalonia to prevent it from spending money.

Catalonia's pro-separatist government challenged the measure in Spain's Supreme Court but a court spokeswoman told AFP it was "in force" and would not be suspended while judges rule on its legality.

READ MORE: The case against Catalan secession

Spain's regions pay taxes to the central government and are then given a quota to spend on healthcare, education and public infrastructure.

Catalonia, which is roughly the size of Belgium and home to around 7.5 million people, receives about 1.5 billion euros ($1.8bn) a month from Madrid to cover essential services.

About a quarter of Catalonia's revenues comes directly from certain taxes which it collects itself as well as from university tuition fees.

READ MORE: Defiant Catalan mayors back independence referendum

To prevent the Catalan government from using this money, the Spanish government has asked banks to control all movements in the accounts and credit cards managed by Catalan leaders.

Opinion polls show Catalonia's roughly 7.5 million residents are divided on independence.

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

Over 70 percent of Catalans want a legal referendum on independence to settle the issue.