Catalonia's President, Artur Mas, has written to EU leaders and world powers seeking their support for a vote on independence from Spain.

The appeal comes amid strong resistance to his plan to hold a referendum in November.

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Mas faces strong opposition from Spain's leading political parties (Photo: iSabadell)

Spain's governing centre-right Partido Popular and the opposition PSOE have both said it would breach the Spanish constitution.

When Mas told media last month that separatist parties had agreed on the referendum questions and on its "consultative" rather than legally binding nature, the Spanish justice minister, Alberto Ruiz-Gallardon, said: "The poll will not be held."

In an interview published on Wednesday (1 January), Spain's economy minister, Luis de Guindos, added: "There is no national investor who considers that there may be a secessionist process in Catalonia at this time."

But for his part, Mas believes he has both the mandate and the legal means to secure a vote.

Separatist parties dominated snap elections in Catalonia in November, with politicians who favour the region's “right to decide” taking some two thirds of the 135 seats in the Catalan parliament.

"Contrary to some reports, there are a number of legal and constitutional options which allow this referendum to take place in Catalonia," Mas said in a letter to German Chancellor Angela Merkel, which was sent in December, but made public on Thursday.

"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 added.

He also said that Catalonia - which accounts for more than 20 percent of Spain's GDP - is wealthy enough to be a net contributor to the EU budget.

He sent similar notes to the EU's 26 other capitals and to 45 leaders of non-EU states.

The Catalan referendum, if it happens, is to take place less than two months after Scottish voters say whether they want to leave the UK.

As with Scotland, it is unclear whether an independent Catalonia would be required to re-apply for EU membership.

If it does, it might make Catalans more reluctant to pursue independence.

Currently, opinion polls indicate that around 55 percent of Catalans want to leave Spain.

EU leaders have so far remained silent on whether they would endorse the move.

But Mas did not send letters to the EU institutions, which have already taken sides.

In responses to parliamentary questions by MEPs, the European Commission has said Catalonia would have to leave the EU before trying to get back in.