(CN) - The Mine Safety and Health Administration will investigate what caused an explosion in the Upper Big Branch Mine in West Virginia that killed 25 and left four missing, government officials said. The tragedy raised questions about mine owner Massey Energy Company's safety record.
The federal agency had shut at least part of the non-union mine 61 times in the past 15 months, and more than 100 times since 2000, for dangerous safety violations, NBC News reported.
The mine, which is owned Massey Energy Company, was cited for 458 safety violations last year, with 50 of them listed as "unwarrantable failures to comply," the Pittsburgh Post-Gazette reported.
Massey was repeatedly cited for problems with the methane ventilation system and for allowing combustible dust to build up, and was hit with two large fines in January, NBC reported.
The ignition of methane is said to have caused the blast.
Experts say the mine should have been treated as having a "pattern of violations," and that methane should have been sampled every five days.
Massey is still contesting more than a third of the violations at the mine since 2007, according to an analysis by The Associated Press. Massey has paid 16 percent of $1 million in fines proposed in the past year, the AP reported.
The federal government, meanwhile, promised action.
"The federal Mine Safety and Health Administration will investigate this tragedy, and take action," U.S. Secretary of Labor Hilda Solis said in a news release. "Miners should never have to sacrifice their lives for their livelihood."
President Obama said Thursday that he has asked federal mine safety officials to report back by next week on what may have caused the blast.
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