LOS ANGELES • Warner Bros on Tuesday denied its controversial film Joker portrays its murderous outcast villain as a hero, after families affected by the Aurora theatre mass shooting penned an open letter expressing concern.

The much-hyped new Joaquin Phoenix film, billed as a "character study" of Batman's nemesis, has been hailed as an Oscar contender, but has raised concerns that its depiction of mental illness and violence could prove incendiary.

Its release next month comes seven years after a man opened fire in a movie theatre in Aurora, Colorado, showing a late-night premiere of The Dark Knight Rises (2012), killing 12 and wounding 70.

Joker depicts the titular character as a severely depressed young man trying to build a career as a stand-up comic, but who is constantly rejected and beaten down by society until he takes matters into his own - extremely violent - hands.

Five members of victims' families wrote an open letter in Hollywood trade publications on Tuesday.

"When we learned that Warner Bros was releasing a movie called Joker that presents the character as a protagonist with a sympathetic origin story, it gave us pause," it said.

They noted that their real-life tragedy had been "perpetrated by a socially isolated individual who felt 'wronged' by society".

In response, Warner said "neither the fictional character Joker nor the film is an endorsement of real-world violence of any kind".

"At the same time, Warner Bros believes that one of the functions of storytelling is to provoke difficult conversations around complex issues," it added.

AGENCE FRANCE-PRESSE