Officials said six trapped coal miners may never be found, outraging family members of the men who say their loved ones are being left for dead.

Searchers were grim Sunday after receiving air readings from a fourth hole drilled more than 1,500 feet into the mountainside. The readings detected insufficient oxygen to support life.

Repeated efforts to signal the men have been met with silence.

"It's likely these miners may not be found," said Rob Moore, vice president of Murray Energy Corp., co-owner of the Crandall Canyon Mine.

Mine officials had sustained hope for two weeks that the miners would be brought out alive, even after three rescuers were killed and six more hurt in another "bump" inside the mountain.

Family members of the six miners trapped in the initial Aug. 6 collapse accused the mine's owners and federal officials of abandoning their loved ones.

"We feel that they've given up and that they are just waiting for the six miners to expire," said Sonny Olsen, a spokesman for the families, reading from a prepared statement Sunday night as about 70 relatives of the trapped miners stood behind him.

"We are here at the mercies of the officials in charge and their so-called experts. Precious time is being squandered here, and we do not have time to spare," Olsen said.

The families demanded that rescuers immediately begin drilling a 30-inch hole into which a rescue capsule could be lowered. Olsen said the families believe it is "the safest and most effective method to reach" them.

Moore had been far more upbeat earlier in the weekend, but on Sunday he said oxygen readings and video images taken from the fourth hole had changed his mind about the miners' probable fate. Oxygen levels in the hole are just 11 to 12 percent, incompatible with life. Normal oxygen levels are 21 percent.

Workers started Sunday on a fifth borehole into the mountain, more than 2,000 feet down, but Moore said he expected to find insufficient air there, too.

"Our thoughts and our prayers and our deepest sympathies go out to the families — for all those families involved in the two tragedies here," he said.

If tunneling doesn't restart, part of the mine will have been turned into a tomb. Despite that, Moore said there is recoverable coal in other parts of the 5,000-acre mine, and the company expected to resume operations at some point. He said he didn't discuss that prospect with family members.