Officials on Monday indefinitely suspended efforts to save six coal miners as a group of mining experts concluded that the area where the men were trapped was structurally unstable and would probably collapse again.
Robert Murray, chief executive of Murray Energy Corp, co-owner of the mine, said hopes of finding anyone alive were dim, a message he said he had relayed to relatives of the miners.
The miners were trapped on Aug. 6 in the Crandall Canyon Mine.
"I don't know whether the miners will be found," Murray said. "But I'm not optimistic."
A day earlier, relatives of the miners lashed out at officials and the mine's owners, faulting their rescue efforts as insufficient and asserting that that they were simply waiting for the six buried men to die.
A panel of eight mining experts from around the US met on Sunday and Monday, poring over records of seismic activity before concluding that further rescue activities would be unsafe.
Richard Stickler, a federal mining official who announced the panel's findings, said that if any of the miners were discovered alive, a hole would be dug to send a rescuer down to lift out survivors.
"The significant risk is unacceptable to send a rescuer miner underground for the purpose of exploration," said Stickler, an assistant secretary of labor and director of the US Mine Safety and Health Administration.
On Sunday, family members issued a statement saying Murray had promised to remove the miners dead or alive
Rescuers have drilled four holes into the Utah mine. A fifth hole, started on Sunday, had reached a depth of 259m by late afternoon on Monday, Stickler said, and was expected to reach its final depth of 621m by 5pm yesterday.
But earlier air samples found oxygen levels too low to support human life. Fresh air was being pumped into the holes, Stickler said, though a camera and sensors lowered last week detected no sign of life.