US Attorney General William Barr said he’s “appalled” that Jeffrey Epstein was able to kill himself while in federal custody, as the FBI announced Saturday that it would be probing the convicted pedophile’s death.

“Mr. Epstein’s death raises serious questions that must be answered,” Barr said.

“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,” Barr added.

The stunning developments come a day after a trove of newly unsealed documents implicated a number of powerful people in Epstein’s alleged sex trafficking ring.

The federal Bureau of Prisons said that the disgraced financier, who was charged last month with trafficking girls for sex, was found unresponsive in his cell around 6:30 a.m. Saturday.

The statement also called Epstein’s hanging death in the Metropolitan Correctional Center’s 9 South Wing “from apparent suicide.”

The BOP said its staff immediately began attempting life-saving measures. Epstein was rushed to New York Downtown Hospital around 7:30 a.m., where he was pronounced dead.

Newly unsealed documents in a civil case between an Epstein accuser and his longtime gal pal, Ghislaine Maxwell, accused a number of prominent men — including Prince Andrew, the late MIT professor Marvin Minsky, former Maine Sen. George Mitchell, ex-New Mexico Gov. Bill Richardson and money manager Glenn Dubin, and lawyer Alan Dershowitz — of using her for sex.

The men or their surviving spouses all denied the accusations.

Lawyers for Epstein did not respond Saturday to requests for comment.