Three employees at Tucson's University Medical Center have been fired for accessing confidential medical records of victims in Saturday's shooting rampage, hospital officials said Wednesday.

The hospital said it notified families of the affected patients.

The shooting killed six people and injured 13, including U.S. Rep. Gabrielle Giffords. Giffords is in critical condition with a bullet wound to the head.

All six remaining injured patients from the shootings, including Giffords, are at UMC.

Hospital officials stressed that they were not aware of any confidential patient information being released publicly.

"The hospital has terminated three clinical support staff members this week for inappropriately accessing confidential electronic medical records, in accordance with UMC's zero-tolerance policy on patient privacy violations," says a statement that UMC officials issued Wednesday.

A contracted nurse also was fired by the nurse's employer, officials said.

Hospital spokeswoman Katie Riley would not say how many patients were affected by the breach, but she confirmed it involved records of patients connected with Saturday's shooting.

"Any potential breaches of patient privacy by UMC staff will be investigated and appropriately addressed," the hospital statement says. "With advances in technology, ensuring patient privacy has become the focus of hospitals nationwide. UMC uses sophisticated technology to help prevent and detect inappropriate access to patient information."

- By Stephanie Innes