Two US doctors are being investigated by the Drug Enforcement Administration over the prescribing of the powerful painkillers Oxycontin and Vicodin to Australian actor Heath Ledger, according to news reports.

The autopsy done after the 28-year-old Australian actor was found dead in his New York apartment late last month, showed that he died of an accidental overdose of six prescription drugs, including the two painkillers, sleeping pills and anti-anxiety medication.

The investigation is focusing on two yet-unnamed doctors, one in California and another in Texas, who provided the Brokeback Mountain actor with the prescriptions.

Authorities are now interested in finding out if the drugs were illegally prescribed, according to the New York Daily News.

It's a standard procedure any time there's a death due to pharmaceutical drugs for the DEA to work with local authorities to see if there's any violation of federal law, the DEA spokesman said.

Even if it was not a celebrity who died we would still be doing this. The loss of one life due to pharmaceutical drug abuse is one life too many.

Besides Oxycodone and Vicodin (also known as Hydrocodone), autopsy results also showed that Ledger's system contained Diazepam (commonly called Valium), as well as Temazepam, which treats anxiety or sleeplessness; Alprazolam (also known as Xanax); and Doxylamine, a sedating antihistamine often used as a sleeping aid.

It's an ongoing investigation, a source in law enforcement told the paper. It's not clear if there was any wrongdoing.

The National Institute of Drug Abuse reports an estimated 48 million Americans have used prescription drugs for nonmedical reasons in their lifetime. Meanwhile, cases of accidental drug poisoning reported by the Centers for Disease Control and Prevention, have risen 68 percent from 1999 to 2004, a number believed to have only increased in the years since.