A lawyer for embattled US comic Bill Cosby has lashed out at new claims of rape and sexual abuse dating back several decades, saying they have "escalated far past the point of absurdity".

The comments came as Cosby suffered a new setback when a live performance in Las Vegas was cancelled, just days after the plug was pulled on two TV projects.

The Treasure Island casino scratched a show next weekend by the comic, a spokeswoman said.

Another planned stand-up performance in Arizona was also cancelled, as had one in New Jersey, according to local media.

The actor, known for playing a doting father on the popular Cosby Show in the 1980s and '90s, has come under fire in recent weeks over claims made by several women.

"The new, never-before-heard claims from women who have come forward in the past two weeks with unsubstantiated, fantastical stories about things they say occurred 30, 40 or even 50 years ago have escalated far past the point of absurdity," his lawyer Martin Singer said in a statement.

"These brand new claims about alleged decades-old events are becoming increasingly ridiculous, and it is completely illogical that so many people would have said nothing, done nothing and made no reports to law enforcement or asserted civil claims if they thought they had been assaulted over a span of so many years."

He made a plea to the media, saying: "It is long past time for this media vilification of Mr Cosby to stop."

Cosby, who has refused to personally address the claims, was greeted with a standing ovation at a show on Friday in Florida, local media reported, but his next show after that, in Las Vegas on Friday, has been called off.

On Wednesday, US network NBC pulled the plug on a new Cosby sitcom, a day after streaming video service Netflix cancelled a planned special.

The storm engulfing Cosby erupted in October when comedian Hannibal Buress branded him a rapist during a stand-up show in Philadelphia - a clip that went viral.

A number of women have since come forward with accusations that Cosby sexually assaulted them.