Actress Asia Argento has described a report that Harvey Weinstein used ex-Israeli agents to spy on his accusers as "terrifying".
The New Yorker reporter Ronan Farrow has published a story claiming Weinstein used private investigators to try to cover up sexual abuse claims.
The Italian actress and director has accused Weinstein of rape.
Weinstein's spokesperson denied that "any individuals were targeted or suppressed at any time".
In his New Yorker story, Ronan Farrow alleged that the film producer employed two intelligence companies, Kroll and Black Cube, to try to collect information on several women and on journalists trying to expose the allegations.
Black Cube advertises itself as "a select group of veterans from the Israeli elite intelligence units". The New Yorker said they included former members of Israeli spy agency Mossad.
After the story was published, Argento tweeted: "Why didn't I, @rosemcgowan, @RoArquette @AnnabellSciorra speak up earlier? We were followed by ex-Mossad agents. Isn't that terrifying? Very."
Farrow's report alleges that two private investigators from Black Cube, using false identities, met McGowan to "extract information" from her in an effort to stop the publication of abuse allegations. One of the investigators is reported to have posed as a women's rights advocate.
McGowan praised Farrow for his investigation, writing on Twitter that "your words will line the halls of justice".
Ronan Farrow your words will line the halls of justice— rose mcgowan (@rosemcgowan) November 7, 2017
and you thought investigative journalism was dead. No. This is the crescendo in the aria. https://t.co/9aJoNZTkz0— rose mcgowan (@rosemcgowan) November 7, 2017
In a statement, Black Cube told the BBC it was its policy "never to discuss its clients with any third party, and to never confirm or deny any speculation made with regard to the company's work".
But the company said it "does not get involved in family disputes or sexual harassment cases" and "applies high moral standards to its work, and operates in full compliance with the law of any jurisdiction in which it operates".
It added: "Black Cube supports the work of many leading law firms around the world, especially in the US, gathering evidence for complex legal processes, involving commercial disputes, among them uncovering negative campaigns."
Sciorra told the New Yorker that the alleged use of private investigators by Weinstein had scared her "because I knew what it meant to be threatened by Harvey", adding: "I was in fear of him finding me."
The New Yorker also reported that one intelligence firm held a profile of actress Rosanna Arquette, who has also accused Weinstein of sexual harassment.
Weinstein's spokeswoman Sallie Hofmeister dismissed the report, saying: "It is a fiction to suggest that any individuals were targeted or suppressed at any time."