Porn star Ron Jeremy was formally charged with the rape or sexual assault of 21 women and girls, US prosecutors said Wednesday.

Jeremy, who has appeared in more than 1,700 X-rated films since the 1970s, has been the subject of criminal allegations within the adult industry for years.

In June 2020 he was accused of raping three women and sexually assaulting a fourth, and his appearance at a Los Angeles court sparked a wave of further allegations.

The charges date back to 1996 and involve 21 alleged victims between the ages of 15 and 51, Los Angeles county prosecutor George Gascon said Wednesday.

Jeremy, who has previously declared himself "innocent" on Twitter, denied all charges. He faces life in prison if convicted.

The 68-year-old -- whose real name is Ronald Jeremy Hyatt -- appeared in famous adult movies including "Deep Throat II" and "John Wayne Bobbitt Uncut."

With his trademark moustache, he was one of the industry's most recognizable stars among the wider public.

But he has long been dogged by assault claims and barred from industry events in recent years.

After the initial charges were brought against Jeremy in June last year, his attorney Stuart Goldfarb denied all the allegations and insisted his client was "not a rapist."

"Ron -- over the years, because of who he is -- has essentially been a paramour to over 4,000 women. And to allege that he is a rapist is beyond... I mean, women throw themselves at him," he added.

Jeremy is the latest high-profile entertainment industry figure to be investigated for sexual abuse in Los Angeles since the #MeToo movement began in 2017.

A taskforce established to investigate sex crimes in Hollywood has so far focused on at least 20 men in the entertainment industry.

Among them is disgraced movie mogul Harvey Weinstein, who is already serving 23 years in prison in New York, but now faces further charges in California.