An autopsy was conducted on Whitney Houston's remains in Los Angeles Sunday, but officials said afterward her cause of death remained unknown.

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Law-enforcement sources told TMZ the 48-year-old, Grammy-winning pop singer had water in her lungs when she died Saturday at the Beverly Hilton hotel, but the cause of her death would not be determined until the results were obtained from toxicology tests.

The celebrity news Web site said authorities suspect Houston may have fallen asleep or lapsed into unconsciousness in her hotel bathtub and drowned after drinking alcohol and taking Xanax.

Authorities had said bottles of prescription drugs were found in the hotel room where she died. Houston had long battled addictions to drugs and alcohol.

Houston's daughter Bobbi Kristina Brown suffered a "complete breakdown" after learning of her mother's death in Los Angeles, sources told People.com.

The magazine said on its Web site the recording star's 18-year-old daughter was in the lobby of the Hilton about the time Houston was pronounced dead in her room Saturday afternoon when she heard the devastating news.

"[Bobbi Kristina] was screaming: 'What's wrong with her? What's wrong with her?," People.com quoted an unidentified source close to the family as saying.

Bobbi Kristina, whose father is singer Bobby Brown, was taken to Cedars Sinai Medical Center Saturday night "because she was having a complete breakdown," the insider said.

She returned to the hospital a second time Sunday morning.

"She went back to the hospital for the same thing -- stress and anxiety," the family source said. She has since been released, People.com reported.

Pastor Joe A. Carter led congregants in a prayer service Sunday at the Newark, N.J., church where Houston had been a member.

The pastor petitioned "the Lord on behalf of Whitney's daughter, her mother, and the entire Houston family," said a statement posted on the Web site of New Hope Baptist Church.

Houston's mother, Cissy Houston, a renowned performer of gospel and pop music and director of the church's sacred music for more than half a century, had been in touch with Carter who said "she needs our prayers and support," CNN reported.

"Whitney was a mother, a daughter, a sister, and that's the focus that we want to keep in front of everyone today, to continue to lift the family up and respect this time of grief," Carter said.

The history of New Hope Baptist Church is "deeply associated with the power of Whitney's voice and the influence that she's had, not only in this church but across the world," Carter said. "We're saddened at this loss."