Hilton had spent just over 72 hours in her cell when the Los Angeles County Sheriff's Department, citing unspecified "medical reasons," sent her home with an electronic monitoring bracelet on her ankle.

 Her release stunned prosecutors who quickly filed a motion seeking to haul the Hilton hotel heiress back behind bars to complete her sentence for violating probation by driving on a suspended license.

 Los Angeles Superior Court Judge Michael Sauer, who had specifically ordered "no electronic monitoring" for Hilton when he sentenced her to jail on May 4, set a hearing for 9:00 am (1600 GMT) on Friday.

 "The decision whether or not Ms Hilton should be released early and placed on electronic monitoring should be made by judge Sauer, and not the Sheriff's Department," said Jeffrey Isaacs, chief of the City Attorney's Criminal Branch.

 In court papers, prosecutors -- who said they learned about Hilton's release through the media -- accused the Sheriff's Department of violating the court's order and called for it to explain why it should not be held in contempt.

 Hilton, 26, in a statement following her release, thanked the Sheriff's Department and jail personnel "for treating me fairly and professionally."

 "I am going to serve the remaining 40 days of my sentence. I have learned a great deal from this ordeal and hope that others have learned from my mistakes," she said.

 Hilton had reported to the Century Regional Detention Center late Sunday to serve her sentence shortly after a red-carpet appearance at the MTV Movie Awards.

 She would likely have served just half of her sentence as authorities had said she could be freed after 23 days for good behavior.

 Her early release triggered a wave of criticism from civil liberties groups denouncing the move as proof of double standards in the justice system for celebrities.

 "One rule for the rich and famous and different rules for everyone else," said Najee Ali, director of Project Islamic Hope.

 Black civil rights leader Al Sharpton said: "This early release gives all of the appearances of economic and racial favoritism that is constantly cited by poor people and people of color."

 In an interview with the Los Angeles Times, Sheriff Lee Baca defended his department's decision to release Hilton.

 "My message to those who don't like celebrities is that punishing celebrities more than the average American is not justice," Baca was quoted as saying.

 "The problem here is that there is a medical issue and it isn't wise to keep a person in jail with her problem over an extended period of time and let the problem get worse," Baca said, refusing to describe the medical problem.

 "In my opinion, justice is being served by the decision to have her serve her time at home. She would still be in the county jail if it were not for the medical advice," he said.

 But City Attorney Rocky Delgadillo said that Los Angeles jails were well-equipped to deal with the medical needs of inmates and the decision to release her was "puzzling."

 "If law enforcement officials are to enjoy the respect of those we are charged with protecting, we cannot tolerate a two-tiered jail system where the rich and powerful receive special treatment," Delgadillo said.

 A powerhouse on the party circuit, Hilton is widely known for her minidresses, spray-on tan, platinum hair extensions and pouty poses, trading on her image as a "celebutante" -- someone famous for being rich and famous.

 She also released a music album, starred in the reality show "The Simple Life" and appeared in films such as "House of Wax," "Pledge This," and the forthcoming "The Hottie and the Nottie."

Agence France Presse