Huntington, Utah ? Rescuers found no signs of life Saturday after drilling a fourth hole into a collapsed mine where six workers have been trapped nearly two weeks, a disheartening blow in a rescue effort that has killed three other people.

A microphone lowered into the new hole revealed nothing to indicate that anyone was in the cavern, and attempts to communicate with the miners by tapping on a drill bit yielded no response, a federal official said. A video camera was lowered into the hole, but the images have not yet been analyzed.

Underground tunneling has been halted since a mountain “bump” Thursday killed three rescuers and injured six others. Officials had hoped a fourth hole drilled into the mine would finally offer clues to whether the men were alive 1,500 feet below ground. Instead, the results were the same as the three previous tries.

“We did not detect any signals from miners underground,” said Richard Stickler, head of the federal Mine Safety and Health Administration.

Crews spent at least four hours beating on the drill steel and setting off explosives to try to get the miners’ attention, he said.

Stickler said a fifth hole was planned.

“As long as we have hope, we will continue working and doing everything we can. Our goal is to find these miners alive,” he said.

But he acknowledged the challenge of working on a mountain where there have been 23 seismic tremors since the initial Aug. 6 collapse.

“They continue to occur and there’s no way of knowing when they’re going to stop,” he said. “We have never seen a situation like we have at this operation.”

Even if rescuers found any of the six miners alive – an increasingly unlikely prospect, given the amount of time elapsed – it would take weeks to lift them out.

Crews would have to drill a much larger, 30-inch hole and lower a metal rescue capsule, the same method used in 2002 to pluck nine trapped miners from the flooded Quecreek mine in western Pennsylvania.