Eden Prairie-based health care giant says it’s not aware of the launch of any new Justice Department activity as reported by the Wall Street Journal.

UnitedHealth Group (UNH) shares declined more than 11% in premarket trading after The Wall Street Journal reported that the Justice Department has launched a civil fraud investigation into the company’s Medicare billing practices.

UnitedHealth Group shares tumbled early Friday on a report that the U.S. Department of Justice has started an investigation into the health care giant’s Medicare billing practices.