Officials in the U.S. state of West Virginia say they hope to get rescuers back into a coal mine to search for four missing miners, after a dangerous build-up of toxic gases forced the rescue teams to evacuate on Thursday.
A mine official said Thursday crews were drilling more boreholes into Massey Energy Company's Upper Big Branch Mine to help release the methane and carbon monoxide that have hampered rescue efforts over the past days.
An explosion killed 25 people there on Monday, the worst U.S. mining disaster in 26 years. So far seven bodies have been recovered from the mine and authorities are trying to recover the bodies of 18 others confirmed dead.
About 32 workers with gas masks entered the mine early Thursday to begin an eight kilometer trek through the mine before they were forced to return to the surface. Officials said it may be Thursday evening before they can try again.
The rescuers are trying to reach a chamber about 300 meters underground, where they believe the missing miners are located.
Officials say they are hoping against the odds the men survived the powerful blast and reached an airtight rescue chamber.
Rescuers banged on pipes Wednesday, but have heard no signs of life in the mine since the blast.
Officials say a build-up of methane gas most likely caused the explosion. The gas is highly flammable and frequently found in coal mines.
Federal officials say they will fully investigate a lengthy record of safety violations by Massey Energy. The company was fined $900,000 last year for violations at this one mine.
This is the deadliest mine accident in the U.S. since 1984, when 27 workers were killed in a fire in Utah.
Some information for this report was provided by AP.