The U.S. Justice Department is investigating UnitedHealth's Medicare billing practices, the Wall Street Journal reported on Friday, while the health insurer said it was unaware of any new probe underway.

The probe is analyzing the company’s practice of frequently logging diagnoses that trigger larger payments to its Medicare Advantage plans, according to a report.

The Justice Department has launched a civil fraud investigation into UnitedHealth Group's Medicare billing practices. The probe focuses on how the company records diagnoses that increase federal payments to its Medicare Advantage plans.