In a filing with the Securities and Exchange Commission, UnitedHealth said it has "full confidence" in its practices. It added that a court-appointed monitor found no wrongdoing after a decade-long probe into its Medicare Advantage business.

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

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

UnitedHealth shares tumbled Thursday after the health insurance giant confirmed that it’s the subject of a Department of Justice investigation. Monitor these key chart levels.

UnitedHealth Group’s stock fell Thursday after the company confirmed government criminal and civil investigations into its Medicare practices but stressed that it doesn’t expect to be charged with any wrongdoing.

We recently compiled a list of 10 Most Undervalued Healthcare Stocks to Buy According to Analysts. It is the largest U.S. health insurer, operating through its insurance arm (UnitedHealthcare) and health services division (Optum).

UnitedHealth Group is scheduled to report second-quarter results on Tuesday morning, capping a tumultuous first half of the year for the health insurance giant.

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.