Federal drug investigators are probing two doctors over the death of Oscar-nominated actor Heath Ledger, the New York Daily News reported.

The doctors — one in California, one in Texas — are believed to have supplied the "Brokeback Mountain" star with the painkillers Oxycontin and Vicodin, law enforcement sources said. Authorities want to know if the drugs were prescribed illegally.

"It's an ongoing investigation," a law enforcement source told The News Tuesday. "It's not clear if there was any wrongdoing."

The New York City medical examiner ruled Ledger, 28, died on Jan. 22 of an accidental overdose of six prescription drugs, including the two painkillers, sleeping pills and anti-anxiety medication. The federal Drug Enforcement Administration has subpoenaed the medical examiner's findings as part of its probe into the doctors, the sources said.

People magazine claimed to have confirmed the Daily News' report.

"We are investigating doctors in Los Angeles and Texas with regard to Ledger’s prescriptions," a source told People.

The subpoenaing of Ledger's autopsy results by the Drug Enforcement Administration was reported shortly after the findings of the report were announced. On Feb. 6, it was said that the DEA would look into the source of the actor's prescriptions.

Click here for the Daily News report.

Click here for the People report.

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.