The 66-year-old, who in July was accused of orchestrating a sex-trafficking network involving girls as young as 14, was last month found unconscious on the floor of his cell with marks on his neck, an episode officials were investigating as either a possible suicide attempt or assault.

Despite that, Epstein was not under suicide watch at a special part of the Metropolitan Correctional Centre in New York City, Reuters reported. Attorney general William Barr has ordered an investigation by the FBI and the prisons’ inspector.

The report that the man who once counted rock stars, politicians and royalty among his circle was not on round-the-clock surveillance emerged after officials revealed his body was found early on Saturday morning in his cell in a special section of the correctional centre. He was transported to a nearby hospital where he was pronounced dead.

There was no immediate explanation for why the ex-financier was not placed under special surveillance.

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“I was appalled to learn that Jeffrey Epstein was found dead early this morning from an apparent suicide while in federal custody,” said William Barr, the attorney general.

“Mr Epstein’s death raises serious questions that must be answered. In addition to the FBI’s investigation, I have consulted with the inspector general who is opening an investigation into the circumstances of Mr Epstein’s death.”

His death came a day after new legal documents, unsealed by a court, provided more details about the numerous young girls Epstein is said to have abused over several decades.

Trump comments on relationship with Jeffrey Epstein: 'I was not a fan of his'

The documents related to a defamation lawsuit brought by Virginia Giuffre, who said she was abused by Epstein and members of his circle over a number of years.

Among those with whom she claimed she was told to have sex were former New Mexico governor Bill Richardson, financier Glenn Dubin, former senator George Mitchell and modelling agent Jean Luc Brunel. All have denied the claims.

Also contained in the documents were accusations by another alleged victim, Johanna Sjoberg, who said Prince Andrew touched her breast while sitting on a couch inside Epstein’s Manhattan apartment in 2001.

Buckingham Palace has repeatedly said the allegations about the Duke of York were “categorically untrue”, despite the men remaining friends even after Epstein served jail time for a 2008 plea of sex with an underage girl.

A Buckingham Palace spokesperson said: “This relates to proceedings in the United States, to which the Duke Of York is not a party. Any suggestion of impropriety with underage minors is categorically untrue.” Prince Andrew is known to have gone on holidays with Epstein up until around 2010.

In the legal papers, Ms Sjoberg said: “I just remember someone suggesting a photo, and they told us to go get on the couch. And so Andrew and Virginia sat on the couch, and they put the puppet, the puppet on her lap.”

Also included among Epstein’s circle was Donald Trump, who in 2002 told New York magazine: “I’ve known Jeff for 15 years. Terrific guy. He’s a lot of fun to be with. It is even said that he likes beautiful women as much as I do, and many of them are on the younger side. No doubt about it – Jeffrey enjoys his social life.”

When fresh charges were brought against Epstein, the president claimed he had not been close and was “not a fan”, despite the emergence of video showing them a party together in 1992 at Mr Trump’s Mar-a-Lago estate.

Cameron Lindsay, a former warden who ran three federal prisons, said the death represented “an unfortunate and shocking failure, if proven to be a suicide”.

“Unequivocally, he should have been on active suicide watch and therefore under direct and constant supervision,” he said. “When you have an inmate as high profile as Epstein, it’s absolutely imperative the warden set the tone with his or her leadership to ensure these kinds of incidents don’t happen.”