William Barr, the US attorney general, on Monday said he was “appalled” and “angry” over alleged child sex abuser Jeffrey Epstein’s death in custody as new claims emerged about oversights from prison guards.

Epstein, who was found dead in a New York prison cell on Saturday in an apparent suicide, was also alone in his room when he died, according to a senior prison union official, despite procedures that he should have been accompanied by another inmate.

The criticism came as French government ministers demanded that the country's prosecutors launch their own investigation into Epstein, saying the US inquiry had exposed the disgraced financier’s links with France.

Epstein is believed to have visited France frequently, with US authorities saying Epstein had a residence in Paris, described by French sources as a luxury apartment on the Avenue Foch, one of the capital’s most expensive streets, favoured by royalty, celebrities and billionaires.

He also maintained homes in the seaside resorts of Nice and Biarritz, according to the sources.

Epstein, 66, was arrested on July 6 in New Jersey after his private jet landed on a flight from Paris. He was charged with sex trafficking underage girls but died before the case went to trial.