Results of a post-mortem on Hollywood star Heath Ledger are inconclusive, US authorities said today.
The 28-year-old actor was found dead at his New York apartment yesterday.
Police are treating his death as possibly drug-related and said sleeping pills were found close to his body.
But a spokeswoman for the medical examiner's office said an autopsy had proved inconclusive and further tests were needed - which could take around 10 days.
There were unconfirmed reports today that the 'Brokeback Mountain' star was suffering from pneumonia at the time of his death.
The actor's family have said that his death was a tragic accident.
Reading a statement outside the family home in Perth, his father Kim said: "We, Heath's family, can confirm the very tragic, untimely and accidental passing of our dearly loved son, brother and doting father of Matilda."
New York Police Department spokesman Paul Browne said: "We are investigating the possibility of an overdose... There were pills within the vicinity of the bed." He added that the prescription medicine included sleeping pills.
The star's housekeeper found him at 3:26pm (US time) yesterday, and tried to wake him for his appointment with a masseuse.
Paying tribute to Heath Ledger, Australian Prime Minister Kevin Rudd said: "Heath Ledger's diverse and challenging roles will be remembered as some of the great performances by an Australian actor."
The actor's compatriot and 'The Patriot' co-star Mel Gibson said: "I had such great hope for him. He was just taking off and to lose his life at such a young age is a tragic loss."
Australian actress Nicole Kidman said: "What a terrible tragedy. My heart goes out to his family."
The bosses of Warner Bros, Alan Horn and Jeff Robinov, said: "The studio is stunned and devastated by this tragic news. The entertainment community has lost an enormous talent. Heath was a brilliant actor and an exceptional person. Our hearts go out to his family and friends."
Ledger was nominated for an Oscar for his part in the film 'Brokeback Mountain' and had recently finished work on the Warner Bros blockbuster 'The Dark Knight'.
Last year he broke up with actress Michelle Williams, who played his wife in 'Brokeback Mountain' and was the mother of their two-year-old daughter.
The actor had recently been working on 'The Imaginarium of Doctor Parnassus' with director Terry Gilliam; they previously collaborated on 'The Brothers Grimm'.
To view our photo gallery on the life and career of Heath Ledger click here.
