Ralph Fiennes has defended Harry Potter author J.K. Rowling, insisting he "doesn't understand the vitriol directed at her".

The writer faced huge backlash last year for questioning the notion that "sex isn't real", and raised concerns about changes to gender identity laws - infuriating transgender activists and leading to many of the stars of the Harry Potter movies, which are based on her boy wizard books, issuing statements to make it clear they didn't agree with her stance.

However, Fiennes - who played Lord Voldemort in the film adaptations of Rowling's novels - has told Britain's Daily Telegraph newspaper that he's bemused by people's level of fury towards the author.

"I can't understand the vitriol directed at her," he said. "I can understand the heat of an argument, but I find this age of accusation and the need to condemn irrational. I find the level of hatred that people express about views that differ from theirs, and the violence of language towards others, disturbing."

Fiennes' remarks are in direct contrast to those of Daniel Radcliffe, Emma Watson, and Rupert Grint - the three main stars of the movies - who all distanced themselves from what Rowling said and stood up for transgender rights.

Rowling has denied being transphobic on multiple occasions.