UnitedHealth Group confirmed Thursday the company is facing criminal and civil investigations from the Department of Justice (DOJ) related to its Medicare billing practices. The health care giant said in a securities filing and subsequent statement it has begun complying with formal criminal and civil requests.

UnitedHealth Group says it is cooperating with federal criminal and civil investigations involving its market-leading Medicare business.

Shares of UnitedHealth Group fell sharply in premarket trading Thursday after the healthcare giant said it was “complying with formal criminal and civil requests” from the U.S. Department of Justice.

UnitedHealth Group has said it is under investigation by the Department of Justice, which is probing its involvement in Medicare, a federal health insurance program for those over 65 and people with disabilities. Newsweek reached out to the Department of Justice for comment.

The health-care giant said it has started complying with both criminal and civil requests from federal investigators and it was cooperating with them.

Stocks were mixed Thursday and the Dow Jones Industrial Average declined following slumps in Honeywell and IBM after the companies issued quarterly earnings updates and as UnitedHealth Group traded lower after saying it was “complying with formal criminal and civil requests” from the U.S. Department of Justice.

Mizuho's Jared Holz joins 'Fast Money' to talk the future of UnitedHealth after the stock slides on news of DOJ probe.