Officials in the U.S. state of West Virginia have withdrawn rescue workers from a mine where four miners remain missing after an explosion this week that killed 25 people.
West Virginia Governor Joe Manchin told reporters Friday the rescue workers pulled back running into smoke from a fire. Before leaving, the crews reached one of two airtight chambers where it was hoped the trapped miners could have taken refuge, but they found no one there.
Workers are now drilling holes from above to lower a camera near the second chamber, and safety official Kevin Stricklin says fire-retarding nitrogen gas will be pumped into the area.
The missing men have not been contacted since the explosion on Monday, and hopes rest on their having reached one of the survival chambers. Those compartments only carry a four-day supply of oxygen, food and water.
Seven bodies have been recovered since the explosion on Monday that triggered the worst U.S. mining disaster in almost 30 years. Crews also are trying to reach the bodies of 18 others confirmed dead.
President Barack Obama asked federal mine safety officials Thursday to study possible causes of the disaster and report to him next week.
Officials say methane gas most likely caused the explosion at the Upper Big Branch mine in Montcoal, West Virginia. The highly flammable gas is often found in coal mines.
Massey Energy Company, which owns the mine, was fined $900,000 last year for safety violations at the facility.