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UnitedHealth Group

revealed Thursday it is facing Department of Justice investigations over its Medicare billing practices, adding to a string of setbacks for a company that owns the nation’s largest and most powerful private insurer.

In a securities filing, the company said that it has started complying with formal criminal and civil requests from the DOJ, and that it reached out to the department after reports of the probes surfaced. UnitedHealth also said it has launched a third-party review of its business policies and performance metrics.

The company told CNBC that it expects to complete that review toward the end of the third quarter.