Pharmacy used by Michael Jackson may have supplied Whitney Houston with pills

Coroner confirms singer was found by make-up artist amid reports of empty medication bottles

Tributes to the singer on a Grammy street plague (AP)

Whitney Houston was underwater and unconscious when staff found her in the bathtub of her Los Angeles hotel suite, police confirmed last night, amid mounting speculation about the role prescription drugs may have played in her death.

The room at the Beverly Hilton hotel where the 48-year-old singer was discovered on Saturday afternoon contained several bottles of pills, they revealed. But it remains too early to speculate about whether they contributed to her demise.

"She was underwater and apparently unconscious," said Lt Mark Rosen, of Beverly Hills police. "Ms Houston was pulled from the [bath] tub by members of her staff and hotel security was promptly notified."

Cardio-pulmonary resuscitation was immediately performed, but it was too late to revive her and she was pronounced dead at 3.55pm. A post-mortem examination did not reveal obvious signs of trauma or foul play, but no official cause of death will be announced until toxicology tests are completed, a process likely to take between six and eight weeks.

Earlier, the showbusiness website TMZ reported that a range of painkillers and sedatives, including Xanax, Ibuprofen, Amoxicillin and Midol, were recovered from the scene. Some had been obtained from the Mickey Fine clinic in Beverly Hills, a location famous for supplying Michael Jackson with medication.

Houston was last seen by staff an hour before her body was discovered by a make-up artist who went into the bathroom to see what had become of her. Investigators must therefore establish whether the singer died from drowning or was killed by an event such as a heart attack before slipping under the water. Detectives will also scrutinise her state-of-mind in the days leading up to her death, in which she was observed behaving erratically. Until the investigation is completed, "our intent at Beverly Hills Police Department is not to fuel the speculation or rumours that are circulating," Lt Rosen added.

Houston's death on Saturday, hours before a pre-Grammy party, overshadowed Sunday night's awards, which included several moving tributes and attracted 39 million viewers – the event's highest figures since the mid-1980s.

Her body has been released to her family, and a funeral is expected to be held in the coming days in Houston's native New Jersey. Meanwhile, Sony – Houston's record label – has responded to her untimely demise by almost doubling the price of her greatest hits album on iTunes.