Federal regulators failed to protect workers at Utah's Crandall Canyon mine, where nine people died last summer, a U.S. Labor Department watchdog said Monday.

The department's inspector general's office blamed federal mining regulators for negligence in approving a roof-control plan for the mine. Six miners died in a collapse Aug. 6, and another cave-in 10 days later killed three people trying to reach the trapped men.

The 80-page report Monday from Assistant Inspector General Elliot Lewis said the Mine Safety and Health Administration could not show it made the right decision when it approved risky retreat mining at Crandall Canyon.

Click here to read the report (PDF).

Retreat mining involves yanking supporting pillars of coal from the mine and allowing the roof to collapse as miners and equipment work their way out.

In the same report, MSHA director Richard Stickler disputed the claim his agency was negligent and unduly influenced by the mine operator, Ohio-based Murray Energy Corp. MSHA is part of the Labor Department.

"We take exception to the inspector general's use of headline-grabbing language that is unsupported by facts or evidence," MSHA spokesman Matthew Faraci said Monday.

The report placed much of the blame on MSHA's field office in Price, Utah, and said agency headquarters exercised little or no oversight.

The field office, it said, ignored Crandall Canyon's history of mining-induced collapses by failing to check with the University of Utah's Seismograph Stations, which had registered the ground's movement.

The U.S. Bureau of Land Management, which leases federal land for mining, doesn't have to ensure safety but consistently raised questions about risks at Crandall Canyon, according to the report.

"Thing(s) should get interesting soon," a BLM inspector wrote of cave-in dangers on July 12, less than a month before the disaster.

The bodies of the six miners killed in the first collapse have not been recovered from about 1,900 feet underground.

"The inspector general's report highlights the fact that miners performing retreat mining in this country remain at serious risk because of MSHA's deeply flawed process," said Rep. George Miller, D-Calif., chairman of the House Education and Labor Committee.

Miller took the opportunity Monday to promote legislation awaiting Senate approval that he said would strengthen government reviews for retreat mining.

The inspector general's office said it didn't try to determine the reasons for the mine collapse. Instead, the report blamed MSHA for failing to adequately show the mining practice was safe, saying the agency's decision lacked documentation and transparency.

"Today's report confirms that MSHA clearly failed to fulfill its duty to protect the Crandall Canyon miners," said Sen. Edward Kennedy, D-Mass, chairman of the Senate Health, Education, Labor and Pensions Committee. Kennedy had requested the report.

The report recommended nine policy changes to MSHA Director Richard E. Stickler, who said his agency was acting on the suggestions.

"We don't take any issue with the recommendations," Faraci said.

MSHA officials were perturbed at the report's assertion that MSHA agency couldn't prove it was free of Murray Energy's influence when it signed off on the retreat mining.

In a statement with his report, Lewis made clear he wasn't implying that regulators were unduly influenced, an acknowledgment MSHA officials said they welcomed.