Actor Sylvester Stallone has denied allegations that a 16-year-old fan accused him and his bodyguard of sexually assaulting her in the 1980s.

The accuser claimed the Rambo star said he would "beat her head in" if she revealed the incident, which took place in a Las Vegas hotel room, according to a police report published by several media outlets.

The girl told authorities she was left "humiliated and ashamed" by the incident, so declined to press charges, the report states.

Michelle Bega, a spokeswoman for Stallone, 71, said on Thursday: "This is a ridiculous, categorically false story.

"No one was ever aware of this story until it was published today, including Mr Stallone. At no time was Mr Stallone ever contacted by any authorities or anyone else regarding this matter."

The actor's denial followed a report in the Mail Online, but Bega declined to comment when asked if Stallone was aware of the allegations when they were previously published by the Baltimore Post-Examiner in February last year.

According to the Mail Online, John Samolovitch, a retired Las Vegas Metropolitan Police Department detective sergeant, confirmed the documents' authenticity.

The police report said the girl alleged she met Stallone in 1986 in the Las Vegas Hilton Hotel when she asked for an autograph. She claimed a bodyguard gave her keys to a hotel room where she later had sex with both men on July 26.

"She said that after she got dressed, Stallone made the comment to her that they were both married men and that she could not tell anybody about the incident and if she did, that they would have to beat her head in," the officer wrote.

A second report from the sexual assault unit said the girl initially thought it was a joke, but "became very distraught and frightened, and wasn't sure that threat had been a joke after all" after she left the room.

The document said the girl was not physically forced to have sex but felt "intimidated."

Stallone's denial follows a string of high-profile sexual harassment allegations against Hollywood stars, including Harvey Weinstein, Kevin Spacey and Louis CK.