Rescue crews at a West Virginia coal mine have found no more survivors, and all 29 workers trapped in an explosion are confirmed dead, officials said early Saturday.

Families, colleagues and officials had been holding out hope that four unaccounted for miners might be found alive inside one of the mine's safety chambers, but rescuers who checked those shelters Friday found neither had been activated, state Gov. Joe Manchin confirmed at a briefing.

"None of the chambers had been deployed, and none of our miners suffered, so this journey has ended, and now the healing has started," Manchin said.

West Virginia Gov. Joe Manchin, left, and Kevin Stricklin of the Mine Safety and Health Administration speak to the media Friday. (Bob Bird/Associated Press)

"We made sure that we have a total count for every miner that was in that mine. The bodies of our miners were found."

In the immediate aftermath of Monday's explosion at the Upper Big Branch-South mine, it was known that 25 workers had died, while the status of the other four was unknown. Rescuers spent the next five days attempting to get underground to search for the men, hoping that they had taken refuge in one of the survival chambers.

The first two rescue attempts were aborted when crews encountered dangerously high levels of carbon dioxide and explosive methane in the mine. Workers spent several days drilling vent holes underground to release the gases.

Crews re-entered the mine, about 50 kilometres south of Charleston, W. Va., around 1 a.m. ET Friday. They were able to check one airtight chamber for survivors, but the chamber was empty.

The crews moved through a shaft to try to reach a second chamber, but they were forced to retreat when they saw smoke and signs of a fire somewhere in the mine.

When they reached the second chamber late Friday night, they discovered it, too, had not been activated.

The bodies of the four missing miners were found "exactly where we thought" they might be, Manchin said.

Safety officials investigate

U.S. President Barack Obama has asked federal mine safety officials to report next week on what caused the deadly blast.

The mine is operated by Performance Coal Co., a subsidiary of Virginia-based Massey Energy Co., the fourth-largest coal mining company in the United States. Over the past year, Massey Energy was fined $329,000 US for several serious violations involving its ventilation plan and equipment at the Upper Big Branch Mine.

On the day of the blast, the Mine Safety and Health Administration cited the mine for two safety violations: one involving inadequate maps of escape routes, the other concerning an improper splice of electrical cable. However, Stricklin said those violations had nothing to do with the explosion.

On Thursday, Massey CEO Don Blankenship continued to defend his company's record and disputed accusations from miners that he puts coal profits ahead of safety.

But in an interview last June for the web series Focus Washington that surfaced this week, Blankenship said that "so many of the laws" on mine safety are "nonsensical from an engineering or coal mining perspective."

"A lot of the politicians, they get emotional, as does the public, about the most recent accident, and it's easy to get laws on the books," he continued.

Blankenship's stance provoked a firm rebuke from Cecil Roberts, president of the United Mine Workers of America union, which doesn't represent any employees at the Upper Big Branch Mine.

"I've seen where Massey's CEO, Don Blankenship, equates criticizing his or Massey's safety record to being against coal and coal jobs," Roberts said in a statement. "I'm here to tell Don that's bull."

Roberts added that his union has tallied 45 deaths — not including the four miners whose bodies were only found Saturday — at Massey-owned mines in the last 11 years.

"No other coal operator even comes close to that fatality rate during that time frame," Roberts said. "That demands a serious and immediate investigation by MSHA and by Congress."

The death toll of 29 in Monday's blast is the worst U.S. coal mining catastrophe since a 1970 explosion killed 38 in Hyden, Ky.

With files from The Associated Press