Federal officials decided to indefinitely suspend the underground search for six trapped Utah miners after three rescue-workers were killed and six were injured during a cave-in.
"Is there any possible way we can continue this underground operation and provide safety for the rescue workers? At this point we don't have an answer," said Richard Stickler, head of the federal Mine Safety and Health Administration.
The workers were tunneling through rubble when the cave-in occurred. Those who survived the Thursday collapse have injuries ranging from broken bones to head and internal injuries.
Outside the mountain, rescue efforts continued. Workers are still drilling a fourth hole, looking for some sign the six men trapped underground since Aug. 6 are still alive.
The crew still has to drill another 900 feet below the surface to reach the mine. They are aiming for a spot where vibrations were briefly detected on Wednesday.
"We hope to find the miners alive when that borehole goes into the mine. We can keep them alive lowering water and food through the borehole," said Stickler.
A camera dropped into the mine showed images of an intact chamber with potentially breathable air, but no sign of survivors.
Nonetheless, there are more questions than answers about what will happen next in the rescue efforts, said CNN's Kate Bolduan told Â鶹´«Ã½net on Friday.
Officials believe the rescue workers were caught in a "mountain bump," where a seismic shift causes coal and rock to shoot from the walls.
"(The rescuers) were about halfway there when this seismic bump occurred," Bolduan said, from the Crandall Canyon mine near Huntington, Utah.
Stickler said mine-safety experts were being summoned to central Utah to discuss the crisis. Gov. Jon Huntsman said there would be a federal investigation into the collapse and that the state would also help with the inquiry.
"Yesterday we went from a tragedy to a catastrophe," Gov. Jon Huntsman said. "We have questions, too, and we want answers to those questions. We want to make sure that the lives that were lost last night were not in vain."
Since the miners were first trapped, rescuers have been delayed by tremors, and more seismic shaking interfered with rescue attempts Thursday morning.
"The seismic activity underground has just been relentless," Bob Murray, chief of Murray Energy Corp., the co-owner and operator of the Crandall Canyon Mine, said Thursday.
"The mountain is still alive, the mountain is still moving and we cannot endanger the rescue workers as we drive toward these trapped miners."
With files from The Associated Press
