CENTERTOWN, Ky. (AP) — The Kentucky surface coal mine where two workers were killed by falling rock was cited earlier this year over the stability of a highwall.

Investigators said Darrel Winstead, 47, and Samuel Lindsey, 23, were killed Friday when a pile of rock crushed their truck as they drove near a highwall.

U.S. Mine Health and Safety Administration records show the agency cited operator Armstrong Coal in April. The citation was first reported by the Owensboro Messenger-Inquirer.

"That was an unrelated incident that took less than an hour to correct," Bob Gunnell, a spokesman for Armstrong, said Saturday.

The citation for the Equality Mine at Centertown refers to standards that require removal of loose hazardous material from the top of highwalls, the unexcavated face of the layers of soil and dirt and rock lying on top of the coal seam.

Records show Armstrong has contested the citation.

Armstrong released a statement expressing condolences for the men and pointing to its safety record.

"The Armstrong Coal Company's Equality Mine has a strong safety record having previously gone 436 days without an accident and winning several awards for safety. Armstrong Coal officials are fully cooperating with state and federal mining officials in their inquiries," the statement said.

The two men were on a blasting crew from a contractor at the mine, MEMSCO, which is based in Dawson Springs and is a subsidiary of Midland Powder Co. of Evansville, Ind.

The accident was the first at the mine since Armstrong took over operation in December 2008, according to the MSHA records. This year Armstrong has been cited five times at this mine.

MEMSCO was cited in July over a standard that lists 30 wide-ranging provisions for vehicle safety. The MSHA records don't indicate which provision led to the citation and show the agency hasn't yet assessed if there was a violation.

Armstrong plans to observe a moment of silence at all its mines at noon Tuesday in remembrance of the two miners.