Beastie Boys vocalist Adam Horovitz has sided with nine women who this week accused his father of sexual harassment and assault.

Playwright and screenwriter Israel Horovitz, 78, faces multiple allegations after the women spoke to the New York Times on Thursday.

“I believe the allegations against my father are true and I stand behind the women that made them,” said Adam Horovitz, better known by his stage name Ad-Rock.

Israel Horovitz resigned from the board of the Gloucester Stage Company, the Massachusetts theatre company where he was founding artistic director, as the allegations became public.

The New York Times published on-the-record allegations in which the women described assaults ranging from forcible kissing to rape.

Some of the allegations were reported in 1993 and published by the Boston Phoenix newspaper without the victims’ names, but at the time the elder Mr Horovitz called them a “character assassination” and Gloucester theatre defended him.

Liz Neumeier, Gloucester’s current board president, apologised for the theatre’s handling of the initial complaints.

“Our hearts go out to the many women who are, once again, reliving the harassment and assaults they endured,” she said in a statement.

“We recognize that in the past their reports were grossly mishandled. The board is united and committed to ensuring that such behavior does not take place at Gloucester Stage and we will take any reports seriously.”

Israel Horovitz has written over seventy plays including Out of the Mouths of Babes and Strong-Man's Weak Child.

He told the New York Times that he had “a different memory of some of these events, [but] I apologize with all my heart to any woman who has ever felt compromised by my actions, and to my family and friends who have put their trust in me.”

The allegations against him emerged in the same week that Matt Lauer, host of the NBC breakfast show Today, was fired over harassment allegations.