BARCELONA (Reuters) - Spain’s electoral commission barred former Catalan leader Carles Puigdemont from running in the European Parliament elections in May, he said on Monday, a day after a general election where the region’s separatism has been a pivotal issue.

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Puigdemont fled Spain in 2017 after Madrid imposed direct rule on the wealthy northeastern region which had unilaterally declared independence. He is living in Belgium.

Puigdemont and two other exiled candidates from his Junts per Catalunya (Together for Catalonia) party said in a statement the commission upheld an appeal against their candidacies lodged by the conservative People’s Party and center-right Ciudadanos.

Nobody at the electoral board was available for comment.

But El Pais newspaper cited its ruling as saying the Catalan party had until the end of Monday to change its electoral list. The move against them was based on the fact they are not registered as Spanish citizens residing abroad, El Pais said.

Puigdemont, Clara Ponsati and Toni Comin called the ruling a “flagrant violation” of their rights and “proof of collusion between the judiciary, which should be independent, and certain political interests”.

They vowed to take legal action in Spain and Europe.

From Belgium, Puigdemont ran for office in the December 2017 Catalan elections and was proposed for regional president by a parliamentary majority, but Spanish courts banned his attempt to assume office from outside the country.

He faces arrest on charges of rebellion if he returns to Spain.

The northeastern region’s independence drive was instrumental in triggering Sunday’s snap general election.

It was a central issue throughout campaigning and could be crucial in determining the composition of the next government.

Spain’s ruling Socialists were weighing options for forming a new government on Monday after they won the election but fell short of a majority in a deeply fragmented parliament. If they seek a coalition partner on the left, that would likely require support from at least one Catalan separatist lawmaker.