Spain's Constitutional Court has annulled Catalonia's unilateral declaration of independence, which the court described as "a serious attack on the rule of law".

The Catalan parliament should note that the right to autonomy "is not and can not be confused with sovereignty," the court said on Wednesday, according to Spanish newspaper El Pais.

Catalonia's regional parliament declared independence on October 27.

The declaration followed the disputed referendum on October 1 that was ruled illegal by Madrid.

According to the Catalan government at the time, 90 percent voted in favour of independence, but turnout was less than 50 percent.

The Spanish government in Madrid fired Catalonia's president and dismissed its parliament hours after the region made the declaration.

Spain later issued an international arrest warrant for Carles Puigdemont, the deposed Catalan leader, and four former Catalan regional ministers.

Puidgemont and his former colleagues turned themselves in to the police in Brussels last weekend and were released from custody a day later.

They are expected back in a Brussels court next week over his possible extradition back to Spain.

Puigdemont is facing charges that include disobedience, sedition and the misuse of public funds.

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He is expected to contest those accusations and has accused Madrid of carrying out a "coup" against the regional government.

Meanwhile, a partial strike shut down several roads across the region on Wednesday.

Protesters held banners reading, "Freedom Political Prisoners, We are Republic", at a demonstration in Sant Jaume square in Barcelona.

Regional elections are set for December 21 in Catalonia and are likely to be the next critical stage in the fight between Madrid and Barcelona.