Three deaths in three days at separate U.S. coal mines raised red flags for the U.S. Mine Safety and Health Administration (MSHA) which urged companies to follow regulations and stay focused on safety.

“Three miners killed on three consecutive days is extremely troubling,” Joe Main, assistant labor secretary for MSHA, said in a prepared statement.

The first death came on Friday, Oct. 4 at an underground mine in West Virginia. It was followed by another Saturday at an underground mine in Illinois, and a third on Sunday at a surface mine in Wyoming, the Charleston Gazette reported.

Main said the fact that the deaths occurred over a weekend “when there may be a greater expectation an MSHA inspector would not be present” is “a red flag.”

The coal mining industry has not had three consecutive days of fatal accidents in more than 10 years, Main said. The last time was Dec. 26-28, 2002, and also included a weekend.

The three deaths came while the federal government was shut down. In its prepared statement, MSHA said that despite the government shutdown, the agency “continues to perform certain activities which, if not conducted, would significantly compromise the safety of human life in the nation's mines.”

In the recent incidents, 62-year-old Roger R. King of Moundsville, WV was killed Friday when he was hit in the head by part of a chain being used during a longwall machine move at CONSOL Energy’s McElroy Mine in Marshall County, WV.

On Saturday, a miner at Alliance Coal’s Pattiki Mine in White County, IL, was killed when an underground cart rolled over and he was pinned underneath it.

And on Sunday, a miner was killed when his bulldozer went over a 150-ft highwall at MidAmerican Energy's Bridger Mine in Sweetwater County, WY.

So far in 2013, 17 U.S. coal miners have been killed on the job, according to MSHA.

Bruce Watzman, a senior vice president for the National Mining Association, said his organization is concerned “anytime there is a loss of life at a mine.” He noted that there were three deaths in a four-day period last month at stone-quarry operations in Missouri, Kentucky and Pennsylvania.

“Mine operators have a responsibility to comply with all applicable federal and state regulatory requirements,” Watzman said in an email to the Charleston Gazette. “While some portion of MSHA’s inspectorate is impacted by the government shutdown, mine operators’ safety activities are not on furlough nor are those of states that have inspection responsibilities.”

Unlike other kinds of workplaces, federal law requires periodic safety and health inspections at all of the nation's coal mines. Under the law, MSHA is supposed to conduct what agency officials call “fours and twos,” which are complete inspections of every underground mine in the country at least once per quarter and of every surface mine at least twice per year.

But during the government shutdown, MSHA is instead conducting only “targeted inspections” that focused on “high-hazard” mines with a history of conditions and practices that have recently caused deaths or serious injuries."

MSHA's shutdown contingency plan called for the agency to send home nearly 1,400 of its 2,355 employees nationwide. The agency was scheduled to focus its furloughs at its Arlington, VA, headquarters as part of an effort to continue as many mine inspections as possible.

Stephen Barr, a labor department spokesman, said that MSHA could not immediately say how many “targeted inspections” have been conducted in the last week because agency staff who would keep such records have been furloughed.