WASHINGTON (CNN) — Federal safety officials negligently approved work plans for a Utah coal mine that collapsed in August 2007, leaving nine dead, a Labor Department report concluded Monday.

The report does not reach conclusions about the cause of the disaster at the Crandall Canyon mine, which killed six miners and three would-be rescuers. But it found that officials of the federal Mine Safety and Health Administration could not demonstrate that it did “everything appropriate” to protect workers in approving a plan for the risky mining technique used at the site.

In a written response, MSHA chief Richard Stickler objected to the use of the term “negligent” and any suggestion that mine operator Murray Energy had pressured the agency into approving the use of what is known as “retreat mining” at Crandall Canyon. Stickler wrote that auditors were unable to back up those implications in their report.