Rescuers scratching away at walls of debris for more than three days were just several hours away from reaching the spot where two of the 65 trapped workers are believed to be located, a federal official said Wednesday.

Federal Labor Secretary Francisco Salazar told the Televisa television network that rescue workers had almost cleared a path that would allow them to proceed through the mine's tunnels. They believe that two of the workers are 50 yards beyond the wall.

"These two people will give us an indication of what it is that could have happened," Salazar said.

Almost three days after a gas explosion filled tunnels with fallen rock, wood and metal, rescuers have found no sign of the workers — either dead or alive — in the Pasta de Conchos mine, 85 miles southwest of Eagle Pass, Texas.

But officials late Tuesday did not rule out the possibility, however slim, of finding survivors.

Coahuila state Civil Protection Director Arturo Vilchis said officials "can't speculate on the condition of the miners."

The lack of news added to the strain on the hundreds of weary relatives of the trapped miners. The family members have camped outside the mine in the bitter cold since Sunday's pre-dawn explosion.

A crowd of about 600 shouted at Vilchis until he took refuge behind a line of five soldiers guarding the entrance to the Pasta de Conchos mine.

"What are you hiding?" shouted one man. "If you don't tell us the truth we will go into the mine ourselves."

Yadira Gallegos, whose brother-in-law is trapped in the mine, accused officials of lying to them.

"They said they would tell us something at three o' clock, but they never came out. We want answers," she said.

The crowd calmed down when two rescue workers emerged from the pit in the evening and urged them to have patience.

"Please understand that conditions in the mine are very dangerous," rescue worker Josue Beltran said, adding that loose bits of debris were still falling down in the pit.

Officials at the U.S. Mine Safety and Health Administration said Tuesday they were sending a truck with specialized equipment for analyzing gas samples and several mining experts to help with the rescue operation. The team should arrive at the mine site on Wednesday afternoon, the agency said.

"MSHA and the entire mining community extend our deepest condolences when miners are in danger," said David G. Dye, the agency's acting administrator.

Mexican officials have said the 65 men were each carrying tanks with only six hours of oxygen, though the workers may have been receiving air through ventilation shafts and oxygen tanks that were scattered throughout the mine.

Some family members panicked when they saw Tuesday editions of the local newspaper La Prensa de Monclova, whose banner headline was a quote from a surviving miner: "They are surely dead."

However, Javier de la Fuente, an engineering contractor with mine owner Grupo Mexico S.A. de C.V., said it was too early to write the miners off.

Asked if they might still be alive, he replied: "Can you tell me what lottery number is going to win tonight?"

Because of fears that electric or gas-powered machinery could spark more explosions, rescuers wearing gas masks and oxygen tanks have had to use picks and shovels to move tons of fallen dirt, rock, wood and metal.

They got through one wall of debris, only to encounter another about 600 yards inside the tunnel early Tuesday. At least two conveyer belt operators may be just beyond the wall, but most of the others were thought to be as far as one to three miles from the mine's entrance.

The workers had been installing wooden and metal supports in four recently dug extensions of the mine when the gas exploded at about 2:30 a.m. Sunday.

At least a dozen other workers near the entrance were able to escape with broken bones and burns.

A power outage briefly struck the ventilation system on Tuesday, but a backup diesel generator immediately kicked in and kept the fans going until power was restored, de la Fuente said.

Consuelo Aguilar, a spokeswoman for the National Miners' Union, called for an investigation into Grupo Mexico's responsibility for the disaster.

Juan Rebolledo, vice president of international affairs for Grupo Mexico, said safety conditions met national and international standards, "but accidents can always happen."

And Pedro Camarillo, a federal labor official, said nothing unusual was found during a routine evaluation on Feb. 7.

As well as mining coal, Grupo Mexico is the world's third-largest copper producer, with operations in Mexico, Peru, and the United States.