Rescue crews drilled through to a pocket in the coal mine where six miners have been trapped, but heard no sound through a microphone that was lowered into the collapsed mine.
The mine's co-owner remained hopeful that the six men were still alive despite the silence.
"I wouldn't look at it as good or bad news. The work is not done," said Bob Murray, chairman of Murray Energy Corp.
Mining officials were able to take an air reading from the pocket and said the air quality was good, with 20.5 percent oxygen, some carbon monoxide and no methane.
"That means if they're alive, they're going to stay alive in that atmosphere," Murray said during a news conference early Friday.
Drilling continued on a wider hole, which could accommodate a powerful camera to provide a view inside the pocket, deliver food and water, and hopefully give a more definitive answer about the miners' fate.
Putin's official spokesman Dmitry Peskov commented on remarks in the US media about failures in launching nuclear-capable missiles in Russia
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