BARCELONA • Spain's Catalonia region has called early regional elections for Sept 27, polls that will serve as a proxy vote on independence and raise tensions with the central government in Madrid.

Catalan President Artur Mas signed a decree on Monday, setting the date for the vote in the wealthy north-eastern region, home to 7.5 million people and accounting for a fifth of Spain's output.

The decree made no reference to independence, but Mr Mas - who already faces criminal charges for staging a mock independence referendum in November despite Madrid's objections - has said that if an alliance of pro-secession parties wins a majority, they aim to split from Spain within 18 months.

"Politically, they will not be normal elections; politically, they are a plebiscite on Catalan freedom and sovereignty," Mr Mas said last week.

The regional government has already started setting up institutions of state, which would go into gear if the pro-independence camp wins. Last week, officials presented plans for a future Catalan tax agency and adopted a decree paving the way for a public credit institution to be turned into a Catalan central bank.

The issue of Catalan independence had fallen off the headlines in recent months, with Prime Minister Mariano Rajoy's government more focused on the challenge in a year-end general election from new anti-austerity party Podemos than from Catalan separatists.

But it returned to the political spotlight last month, after Catalan pro-independence parties set aside their differences and agreed to run on a joint ticket in the regional polls.

A smaller far-left party supporting independence refused to join them, but could prove key to achieving the majority in the regional assembly.

Spain's central government has vowed to oppose Catalonia's moves.

AGENCE FRANCE-PRESSE