Federal authorities are stepping up investigations at Department of Veterans Affairs hospitals due to a sharp increase in opioid theft, missing prescriptions or unauthorized drug use by VA employees since 2009.

That's according to government data obtained by The Associated Press.

Doctors, nurses or pharmacy staff at federal hospitals siphoned away controlled substances for their own use or street sales, or drugs intended for patients disappeared.

Aggravating the problem is that some VA hospitals have been lax in tracking drug supplies. Congressional auditors said spot checks found four VA hospitals skipped monthly inspections of drug stocks or missed other requirements. Investigators said that signals problems for VA's entire network.

Both the inspector general's office and the Drug Enforcement Administration say they have increased scrutiny of drug thefts from the VA.