(Reuters) - The U.S. Justice Department has launched an investigation into UnitedHealth's Medicare billing practices in recent months, the Wall Street Journal reported on Friday, citing people familiar with the matter.

Shares of the company fell nearly 7% to $466.88 in premarket trading.

The new civil fraud investigation is examining UnitedHealth's practices for recording diagnoses that trigger extra payments to its Medicare Advantage plans, including at physician groups the insurance giant owns, the report added.

DoJ and UnitedHealth did not immediately respond to a Reuters request for comment.