(AP) — A Mississippi utility faces a federal investigation over a failed coal-fueled power plant.

The Southern Co. says it was informed Monday that the U.S. Department of Justice has started a civil investigation into the plant that subsidiary Mississippi Power Co. was building.

Southern said Wednesday that it’s negotiating with the U.S. Department of Energy to resolve and dispose of property at its $7.5 billion Kemper County plant. The Department of Energy gave $387 million to build a first-of-its kind plant turning soft coal into a gas and burning it to generate power, while removing carbon dioxide and other pollutants. Mississippi Power lost $6.4 billion when it decided to operate only part of the plant burning natural gas conventionally.

Southern says the investigation is connected to Department of Energy talks.