In a filing with the Securities and Exchange Commission, United Health Group 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.

On Thursday, the giant health care conglomerate announced that it had “proactively reached out” to the Justice Department, after reports of a government investigation had surfaced.