The co-owner of the Utah mine that collapsed more than a week ago praised the families of the six men still trapped, saying that "their strength has come from their belief in their God."
The search for missing coal miners moved toward the back of a mine Tuesday, the ninth day of what one official called a "heartbreaking" ordeal.
Although there has been no sign of the six miners since the Crandall Canyon Mine in central Utah caved in, mine co-owner Robert Murray reported that there were reasons to hope they might still be alive.
"We are all very distraught," Murray told a news conference in the nearby town of Huntington. "It's heartbreaking, it's absolutely heartbreaking, that we haven't found them alive, but we have spared nothing in the way of equipment and whatever it takes to find these miners as quickly as possible."
Officials have said the men could already be dead, crushed more than 1,800 feet (550 meters) below the surface when the mine caved in for reasons that have yet to be determined.
There were reasons to believe they had survived, Murray said, including images from a camera dangled into the mine that showed the roof still intact and the existence of breathable air and potable water.
The images also showed an unidentified miner's tool bag, a conveyor belt and reflectors, but no sign at all of the men themselves.
So far rescue crews have twice used drills to pierce into sections of the mine, hoping to contact the missing men, and both times been met only with silence.
The third hole is was set to drop deeper into the mine, into an area where Murray said the miners may have retreated after the cave-in.
Miners were also burrowing out an escape route big enough for a person, but that effort was going slowly and officials have refused to estimate when the tunnel would be completed. Several parts of the rescue operation have taken longer than expected.
Murray, who has insisted that the mine collapse was triggered by an earthquake despite experts' assertions to the contrary, bristled during the news conference at reporters' suggestions that dangerous or improper mining techniques could have been to blame.
However, he conceded that about a dozen miners working on the large escape tunnel had been reassigned after expressing fears for their own safety.
Murray told Reuters: "We have had some miners that have been working on the rescue effort that have asked to be relieved from working right at where rescue effort is going forward as they have been somewhat frightened to continue to work there.
"If we had any real concerns over safety measures we would not have undertaken this underground rescue."
He said the missing men's families were receiving twice-daily briefings and remained hopeful.
"They're holding up extremely well," Murray said. "Their strength is amazing, and I think it comes from their belief in their God."