Houston, who possessed one of the greatest-ever singing voices and sold more than 170 million records, fought a long and public battle with substance abuse after her career and personal life went off the rails.

She was found dead on Saturday afternoon, at the age of just 48, in her bathtub in a luxury suite of the Beverly Hilton hotel as preparations were under way for the Grammy Awards, the highlight of the music industry calendar.

An autopsy on her body was completed on Sunday but the toxicology probe is said to be ongoing and a “security hold” has been placed on its results, which officials say may not be published for six to eight weeks.

Houston’s body was released Monday by the Los Angeles County coroner’s office, CNN said. Family sources told the network that the body was to be flown to her native New Jersey for a funeral expected on either Friday or Saturday.

Ed Winter, the assistant chief coroner for LA County, earlier refused to speculate on any initial indications found in the star’s blood or urine.

Asked several times if coroners knew the cause of death but were just withholding it from the public, Winter said there might be “a suspicion” of the cause but that everyone must wait for official results to be released.

“You can look at a body and not know what the cause of death is. You might have a suspicion. But the person could have suffered a heart attack or an embolism or something,” he explained.

Celebrity website TMZ said it had learnt from unnamed “family sources” that the singer died from a lethal combination of prescription drugs and alcohol.

The website, citing law enforcement sources, and NBC said several pill bottles were found in the hotel room where Houston died, among them the prescription anti-depressant Xanax and other pain medication.

CBS News cited law enforcement sources as speculating the most likely cause of death was a heart attack or prescription drug overdose.

TMZ said their source had revealed there was not enough water in the singer’s lungs to show drowning as the cause of death -- as had first been rumored -- and that she had died before being submerged in the water.

The LA police department said in a statement Monday that Houston was “underwater and apparently unconscious” when found in the tub by members of her staff. Emergency personnel were unable to revive her.

A friend who saw Houston on Thursday, two days before her death, told CNN that the superstar seemed “upbeat and joyful” and not apparently under the influence of drugs.

But the Los Angeles Times reported that Houston had behaved erratically during an appearance that day at a rehearsal for a Grammy Awards party.

Though she greeted people with a warm smile, she appeared disheveled, with mismatched clothes and dripping-wet hair, the newspaper said.

According to the report, the singer flailed her hands frenetically as she spoke, skipped around the ballroom in a childlike fashion and wandered aimlessly about the lobby.

In a 2009 interview with TV talk show hostess Oprah Winfrey, Houston blamed ex-husband Bobby Brown for many of her problems, admitted that she laced her marijuana with rock cocaine, and revealed that she had spent time in rehab.

Houston most recently checked into rehab in 2011 for drug and alcohol treatment, with her representative telling CNN the singer had “voluntarily entered the program to support her long-standing recovery process.”

Houston’s death, on the eve of the annual star-studded Grammy Awards, led to a grief-stricken outpouring from fans and fellow icons alike.

Sales of Houston’s records have soared after her sudden death, with “I Will Always Love You” the top seller on iTunes and her songs appearing 42 times in the iTunes Top 200.

On Amazon.com on Monday, Houston occupied 10 spots in the top 20 album chart.

Houston’s family issued a statement before the Grammy show, saying: “We are devastated by the loss of our beloved Whitney. This is an unimaginable tragedy and we will miss her terribly.” (AFP)