Actor and comedian Bill Cosby on Monday sued seven women who had accused him of defaming them, saying they lied when they accused him of sexual assault.

The counter-suit, filed in U.S. District Court in Springfield, Mass., contends that the women defamed his "honourable legacy and reputation" by accusing him of sexual misconduct.

​"Relying solely on unsubstantiated accusations, counterclaim defendants have engaged in a campaign to assassinate Mr. Cosby's reputation and character by willfully, maliciously, and falsely accusing Mr. Cosby of multi-decade-old purported sexual misconduct," the 78-year-old actor's lawyers wrote in court papers charging the women with defamation, tortious interference and intentional infliction of emotional distress.

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More than 50 women have come forward to accuse Bill Cosby of sexual assault, 35 of whom documented their stories in a July 27 issue of New York Magazine. (New York Magazine)

Cosby's counter-suit to the lawsuits — first filed in December 2014 and charging him with libel, assault and slander — seeks unspecified financial damages. The suits contend that Cosby slandered his alleged victims by calling them liars when they publicly accused him of sexual assault.

"Bill Cosby appears to be going to war against women who have sued him in Massachusetts and who allege that he has victimized them," said lawyer Gloria Allred, who represents several women who have sued the comedian, though not the people involved in the Massachusetts case.

"Such a tactic will not deter courageous women from fighting the battle against him."

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Lawyer Gloria Allred, left, who represents several women who allege sexual misconduct by Bill Cosby - including former Mrs. America Lisa Christie, right - said Cosby's counter-suit won't 'deter courageous women from fighting the battle against him.' (Danny Moloshok/Reuters)

The sexual assault allegations

More than 50 women have come forward to accuse the actor, best known for his role in the 1980s television hit The Cosby Show, of sexually assaulting them after plying them with drugs or alcohol.

Cosby has repeatedly denied wrongdoing and has never been criminally charged. Many of the alleged incidents occurred decades ago, so the statute of limitations for prosecuting them has long run out.

Cosby testified in 2005 that he had obtained the sedative drug Quaaludes, popular in the 1970s, with the intention of giving them to young women in order to have sex with him, according to court documents unsealed in July as part of a separate legal proceeding against him.