LOS ANGELES (AFP) - A woman who has accused Bill Cosby of sexual assault filed a lawsuit against the beleaguered comedian on Wednesday, accusing the entertainer's camp of defaming her by branding her a "liar". In a filing in Massachusetts, Tamara Green - who says Cosby drugged and attacked her in the 1970s - alleged that the comic's camp had damaged her reputation by dismissing her claims as "absolutely false".

Green's suit alleged that a publicist for Cosby, David Brokaw, had defamed her by stating that the assault had never happened "and therefore that plaintiff lied and was a liar". Green said in the lawsuit that Cosby attacked her in the early 1970s when she was an aspiring model and singer.

After inviting her for a lunch meeting at a Los Angeles restaurant, Cosby duped her into taking pills which he claimed were an over-the-counter cold medicine.

Soon afterwards she began to feel "weak, dizzy, and woozy" and Cosby drove her to her his apartment where he assaulted her despite repeated demands to stop, the lawsuit said.

Green had gone public with her allegations in 2005 in an interview with Newsweek magazine, before speaking out again last month as a slew of other women came forward to accuse Cosby of sexual assault.

On both occasions, Brokaw and a lawyer for Cosby refuted Green's claims by branding her a liar.

Around 20 women have now accused the 77-year-old Emmy and Golden Globe winner of sexual assault and even rape in alleged incidents dating mostly from decades ago. Cosby has strongly denied all the claims.

Cosby is world-famous for his role on The Cosby Show, a popular family sitcom that aired in the 1980s and 1990s.