Catalonia's president has called on European Union prime ministers for support as the region seeks a vote on independence in November this year, the source of an increasingly bitter fight with Spain's central government.

Barroso's answer to Mas: Catalonia's referendum on independence is a Spanish debate

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In letters dating from December and made public on Thursday, Artur Mas urged European powers to encourage a referendum that the centre-right government of Mariano Rajoy says is unconstitutional and it will not allow.

The Catalan struggle is likely to dominate the political agenda this year in Spain, which is slowly emerging from a recession and heading towards a general election in 2015.

"Contrary to some reports, there are a number of legal and constitutional options which allow this referendum to take place in Catalonia," Mas wrote in a 20 December to German Chancellor Angela Merkel, which was reproduced on his official website and is one of 27 sent to European leaders.

"I am confident I can rely on you to encourage the peaceful, democratic, transparent, and European process to which I and a vast majority of the Catalan people are fully committed," he wrote.

Scotland is due to vote on independence this year, though Mas made no mention of the British parallel in his note.

Other than embarassing Spain's central government, the international campaign also has a tactical aim, with Catalan's ruling party and citizens groups eyeing an end-game possibly played out in an international tribunal.

With Rajoy and Mas showing no signs of reaching a political negotiation, Rajoy is expected to use the national parliament and Supreme Court to block any move to hold a referendum.

In that case, Mas may well have to call early elections, likely to be won by the more radical independence party the Catalan Republican Left (ERC), opinion polls show. ERC leaders say they will take their battle for a referendum to an international court if need be.

Separately from the letters to EU leaders, the regional government also sent 45 memorandums to foreign countries in December listing its attractions as an export-led economy at the heart of the EU - of which it wants to remain a member.

Opinion polls have shown mixed support for Catalan independence within the region, with some recently showing only 35% would vote for a full break-away from Spain while others have shown support of close to 50%.

But polls have shown overwhelmingly that Catalans want the right to decide and believe that Rajoy should authorise a vote.