The US Army has reportedly warned servicemen about the possibility of mass shootings at screenings of the Warner Bros. film "Joker", after the FBI identified threats from "incel" extremists.

Service members were cautioned to be vigilant about their surroundings and "identify two escape routes" in the event of a shooting, according to US media reports.

The upcoming "Joker" film is a spin off from the Batman series which follows the origins of the villainous clown character who acts as Batman's sadistic nemesis.

The Army told the website Gizmodo that it was alerted to the threat by the FBI, but said it was unaware of any specific plots or suspects.

The email alert was relayed to its servicemen as a precautionary measure, it said.

FBI agents reportedly circulated the warning after it uncovered social media posts about the film by extremists classified as “incels” - a term which refers to men who are "involuntarily celibate" and blame their situtation on women.

The Army's warning explained that incels “idolise the Joker character, the violent clown from the Batman series, admiring his depiction as a man who must pretend to be happy, but eventually fights back against bullies.”

Reports suggest official identified credible threats to target a movie theatre in Texas during the film's screening.