The families of six miners missing since a tunnel collapsed two weeks ago have been warned the men are probably dead and may never be found.
Bob Murray, co-owner of the Utah mine, said he had told relatives he was "not optimistic they will be found alive".
Some families have accused officials of giving up too soon on the rescue.
Below-ground efforts were halted last week after three rescuers died in a cave-in. The US mine safety body has said the mine is structurally unstable.
No contact has been made with the trapped miners since a tunnel collapsed 1,500ft (457m) underground on 6 August.
Listening devices and cameras lowered into the mine have failed to find signs of life.
Rescue capsule
Above-ground rescue efforts are continuing, with workers expected to finish drilling a fifth hole, reaching 2,039ft into the mine, on Tuesday evening.
"I picture my dad wondering 'Where the hell are they?"
Tests from a fourth hole drilled more than 1,500ft (457m) into the mountainside found the air quality could not sustain life.
Relatives of the trapped miners have called on officials to start drilling a large enough hole to send down a rescue capsule to bring out the men.
Cody Allred, whose father Kerry is among the six missing men, told the Associated Press news agency: "I picture my dad wondering 'Where the hell are they? Any time now'," he said.
Mine safety experts have warned that it would be pointless to send down a capsule without knowing the exact location of the trapped miners and that sending workers down in it to search would put more lives at risk because the mountain is still shifting.
It could, in any case, take weeks to drill the 30-inch (76cm) hole.
Mr Murray, chief executive of Murray Energy Corporation, which jointly owns the mine, said on Monday night he had been "very forthright" in spelling out the situation to the families.
"Their reception with me was not good, but at some point the reality must sink in."
His announcement reflects a shift in tone by mine officials, who initially said they were confident the miners would be found alive.
Speaking on Sunday, Sonny Olsen, a spokesman for the families, told AFP news agency: "We are at the mercies of the officials in charge and their so-called experts. Precious time is being squandered and we do not have time to waste."
'Unacceptable risk'
Richard Stickler, head of the Federal Mine Safety and Health Administration, said the unstable nature of the mine, where seismic activity continues, made it too dangerous to work below ground.
"This means the suspension we have on the underground operation will remain indefinitely," he told reporters on Monday.
"The risk is unacceptable to send mine-rescue teams underground for the purpose of exploration."
Rescue teams had tunnelled about 250m towards the trapped miners, with about 350m to go, when the second accident happened last Thursday.
It was caused by a "mountain bump" - a build-up of pressure inside a mine from overhead rock that forces surrounding rock and coal to shoot out of the walls with great force.
^ Back to top | BBC Sport Home | BBC Homepage | Contact us | Help | ©
~RS~q~RS~~RS~z~RS~34~RS~)