MADRID (REUTERS) - Actor Viggo Mortensen has rebuked Spain's far-right party Vox for featuring in a political tweet the sword-wielding hero Aragorn whom he plays in The Lord Of The Rings.

On the day of Spain's recent election, Vox posted an image of Aragorn, with the Spanish flag and party emblem on his back, charging against an enemy army under banners of left-wing, feminist, LGBT, liberal media and Spanish separatist groups.

"Let the battle begin!" #For Spain", it said.

"You'd have to be pretty ignorant to think that using the character... to promote the campaign of a xenophobic, ultra-right party like Vox would be a good idea," Mortensen wrote in a letter to Spanish newspaper El Pais published on Tuesday (May 7).

"I would laugh at their ineptitude but Vox has won 24 seats in Congress; it's no joke," the 60-year-old Danish-American actor, a fluent Spanish speaker with a home in Madrid, wrote from Los Angeles.

In the April 28 general election, Vox became the first far-right party to secure a significant presence in parliament since dictator Francisco Franco died in 1975.

Warner Bros Spain, which has distribution rights, also responded, saying it did not authorise the use of its copyrighted property in any campaigns.

Mortensen said Vox's message was absurd because in the books Aragorn is "a multilingual statesman who advocates the knowledge and inclusion of the various races, customs and languages of Middle Earth" and should not be associated with the far right.

The Lord Of The Rings book by British author JRR Tolkien is an epic tale of a clash between good and evil in a world inhabited by elves, dwarves, orcs and humans.

The film adaptations, including The Hobbit prequels, have grossed around US$5.8 billion (S$7.9 billion) at box offices worldwide.

There was no immediate response by Vox to Mortensen.