HAZARD, Ky. (AP) -- A bulldozer operator has been killed in an accident at a coal mine in eastern Kentucky.

Office of Mine Safety and Licensing spokesman Jim Carroll said 55-year-old Harold Lee Graham of Campton was pushing debris over a 180-foot earthen wall at a mine site in Perry County about 1:15 a.m. Friday when the accident occurred. The bulldozer he was operating fell over the wall at the International Coal Group mine in Ary.

State investigators are at the scene. Carroll said the mine will be closed pending completion of the investigation.

Graham is the 20th coal miner killed in the United States this year and the third in Kentucky.

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