Heath Ledger at the 78th Academy Awards in March 2006, where he was nominated for an Oscar for best actor in a leading role for his work in Brokeback Mountain. ((Chris Carlson/Associated Press))

Heath Ledger died of an accidental overdose of prescription drugs, the New York City medical examiner's office has ruled.

The results were released Wednesday, as his family was planning a private memorial in his home town of Perth, Australia.

Ledger, 28, was found dead in his Manhattan apartment on Jan. 22.

The medical examiner said he had ingested a mix of prescription drugs, including painkillers, sleeping pills and anti-anxiety medication.

"Mr. Heath Ledger died as the result of acute intoxication by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alparzolam and doxylamine," medical examiner's spokeswoman Ellen Borakove said in a statement.

The drugs are the generic names for the painkillers OxyContin and Hycodan, the anti-anxiety drugs Valium and Xanax, and the sleep aids Restoril and Unisom.

None of the drugs was taken in concentrations high enough to be lethal on their own, the report said, but the combination was deadly.

The actor was reported to have prescriptions from several doctors in the U.S. and the U.K.

Police said there were no illegal drugs in his apartment and no indications that he took his own life.

Ledger is expected to be buried at a private funeral in Perth this week.

Medication has 'hidden dangers': Ledger's father

Ledger's father, Kim, released a statement Wednesday after getting news of the medical examiner's report.

"While no medications were taken in excess, we learned today the combination of doctor-prescribed drugs proved lethal for our boy," Ledger said.

"Heath's accidental death serves as a caution to the hidden dangers of combining prescription medication, even at low dosage."

Ledger's father, mother Sally Ledger Bell and sister Kate arrived in Perth on Tuesday after attending two memorial services in Los Angeles.

Ledger's former fiancée, Michelle Williams, also arrived in the Australian city with their two-year-old daughter Matilda.

In a statement released earlier this week, Williams said: "My heart is broken."

Ledger was nominated for an Academy Award for playing the gay cowboy in Brokeback Mountain.

He was also known for his roles in Monster's Ball and A Knight's Tale.

With files from the Associated Press