Six miners trapped after a tunnel collapse in the US state of Utah may never be found, officials have said.
Church services were held for the miners on Sunday
Tests from a fourth hole drilled more than 1,500ft (457m) into the mountainside found the air quality could not sustain life.
Rescue efforts following the 6 August collapse were suspended after a cave-in left three rescuers dead.
No contact has been made with the six trapped miners since a tunnel collapsed 1,500ft (457m) underground.
Since the first mine collapse, rescue teams had tunnelled about 250m towards the trapped miners, with about 350m to go, when the second accident happened at 1835 (0035 GMT) on Thursday.
Thursday's collapse 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, experts said.
Shift in tone
On Saturday, rescuers banged on a drill bit and set off explosives but their efforts were met with silence.
Engineering experts from around the US gathered at the mine on Sunday to try to find a safe way of reaching the missing men.
A fifth bore-hole will be made in the next few days, reaching 2,039ft into the mine, but officials did not believe there was any greater chance of success than with previous attempts.
Rob Moore, vice president of mine co-owner Murray Energy Corp, said it was likely that if they had died their bodies would never be recovered.
"It's likely these miners may not be found," he said.
Correspondents say there has been a marked shift in tone after days of optimism that the miners would be rescued.