The three women held a press conference with their lawyer, high-profile US attorney Gloria Allred, in Los Angeles to air their claims, which relate to a series of alleged encounters in the 1970s and 1980s.

In one of the cases the victim, Helen Hayes, claims she was drugged and sexually assaulted, but was unable to scream. She woke later to the sight of Cosby clapping his hands and saying: "Daddy says wake up."

She was 17 at the time, she said.

Another of his accusers, Beth Ferrier, admitted to having an extramarital affair with Cosby. After it ended, she said, she was visited by Cosby and felt dizzy after the entertainer prepared her a coffee.

"I believe Mr Cosby drugged me and sexually assaulted me that night," she said. "For years, I did not tell anyone about what he had done to me because I was afraid . . . I felt threatened by him, and I did not think anyone would believe me."

Ms Allred said that many of Cosby's accusers were hampered by the fact that the statute of limitations has passed.

The lawyer has challenged Cosby to sign a waiver, effective for six months, which would allow women to pursue allegations of "sexual misconduct" against him. Alternatively, she suggested he put US$100 million into a fund for potential future payouts.

"Justice demands accountability and if Mr Cosby is found liable, he should be held accountable," Ms Allred said.

Cosby has fought rape accusations for more than a decade. In January 2004 the comedian was accused of sexual assault by a woman he had mentored, Andrea Constand.

Ms Constand filed a civil suit against Cosby and 13 women were listed as potential witnesses at the time. Ms Ferrier said she was one of the "Jane Does" in that lawsuit, which was later settled.

The accusations have scuttled Cosby's television projects and led to cancellations of numerous comedy performances, including two gigs in suburban New York that were scheduled for Saturday.

His attorney has called the allegations discredited and defamatory and was not immediately available for comment.

The story was pushed to the centre of the US media in October this yearafter a clip of comedian Hannibal Buress performing a stand-up set went viral.

In the clip, he describes Cosby as having the "smuggest old black man public persona", noting "yeah, but you raped women, Bill Cosby. So, brings you down a couple notches."

The clip, and the resulting wave of women who have spoken out, has turned into a media firestorm in the US.

Cosby's accusers include:

•  Linda Joy Traitz, who says she was sexually assaulted by Cosby in the early 1970s.
•  Model Janice Dickinson, who says she was drugged and raped by Cosby in 1982.
•  Carla Ferrigno, the wife of actor Lou Ferrigno, who says she was attacked by Cosby at a 1967 party.
• Louisa Moritz, who says she was sexually assaulted in a Tonight Show green room in 1971.
• Theresa Serignese, who claims Cosby drugged and raped her in 1976.

Three more women came forward last month - Kristina Ruehli, who claims her drink was spiked before Cosby assaulted her in 1965, Renita Chaney Hill, who claims she was assaulted by Cosby as a teenager, and Angela Leslie, who claims she was assaulted by Cosby in a hotel room in 1992.

And a lawsuit, filed in November, claims Cosby took Judy Huth, aged 16 at the time, to a tennis club in California, gave her alcohol and then took her to the Playboy Mansion.

Ms Huth says she was then sexually assaulted. She was 15 at the time.

Her lawsuit uses a portion of California law that permits lawsuits up to three years after childhood sex abuse is "discovered" to have caused damages, no matter the plaintiff's age, a hurdle legal experts say will be difficult to clear.

There are now a total of 20 women who have accused Cosby of assaulting them.

A security guard who worked on The Cosby Show, Frank Scotti, also came forward in October to say he organised for eight women to be paid for their silence after alleged assaults.

Mr Scotti, who is now 90, also said Cosby had an arrangement with a modelling company which sent aspiring models to him for "interviews".

Mr Scotti claims he stood guard outside Cosby's dressing room while the interviews took place.

with Reuters