A spokeswoman for Prime Minsiter Mariano Rajoy said the central government has not changed its mind on banning such the vote, which it said would be in breach of the country's constitution.

Rajoy has an absolute majority in parliament which means he can easily reject the secession vote. The main opposition party is also against a referendum.

But the Catalan government said it will still go ahead with the plan.

Latest polls put Catalan support for independence at around 50 percent, but some 80 percent want to vote on the matter.

A few dozen protesters outside the Catalan parliament on Thursday waved independence flags, while a smaller group supported their region staying within Spain.

Seen as the economic powerhouse of Spain, Catalonia has a distinct culture, language and already benefits from the most autonomous rights among Spanish regions.

Similar questions are being raised in Scotland, which also plans to hold a referendum on 18 September.

Were these countries to become independent, legal experts say they would need to apply for EU membership, as they would no longer be covered by the membership treaties of the countries they left.

Scottish legal experts admit that a new EU application will have to be put forward, but they argue that if Scotland becomes independent, there would be some "interim arrangements" with the EU to bridge the transition to membership.