Federal inspectors at the mine where 12 men died after a January explosion said Friday that workers could re-enter all but the abandoned area where the fatal blast apparently occurred.

Ashland, Ky.-based International Coal Group Inc. will resume production at the Sago Mine next week, said Ray McKinney, coal mine safety administrator for the Mine Safety and Health Administration. An ICG spokesman said he could not immediately comment.

Thirteen miners became trapped deep in the mine Jan. 2 after an explosion and were exposed to deadly carbon monoxide for more than 41 hours before searchers found them. By then, all but one had died.

McKinney said his agency has finished its underground investigation of the mine. He declined to speculate on what caused the explosion but said investigators believe its source was by seals on the mined-out area known as Two Left.

MSHA and federal scientists with the National Institute of Occupational Safety and Health are planning to test the 40-inch-thick, dense foam blocks that were used to seal off the area, McKinney said.

Omega blocks, a lighter, cheaper alternative to concrete blocks, are widely used in U.S. coal mining.

McKinney said ICG planned to resume work with two shifts but had few other details on the company's plans.

It was unclear how quickly the company planned to comply with new emergency rules that MSHA adopted to help miners escape future accidents.

The rules that went into effect Thursday require coal companies to comply within 30 days or at least show purchase orders for the necessary equipment.

Companies must give each miner an extra air pack and, in some cases, store additional breathing devices along escape routes. The companies also must ensure miners have clearly marked "lifelines" along escape routes.

Lead investigator Richard Gates said his 10-person team examined the mine's physical condition and equipment, took hundreds of rock dust samples, and conducted 46 private interviews with company officials and employees, with more to come.

Some mine-rescue teams say they have not been interviewed, despite complaints from the victims' families that state and federal officials waited too long to put the rescue teams underground.

Miscommunication among the rescue teams, the command center and observers also contributed to a widespread but mistaken belief that 12 of the 13 trapped miners had survived.

McKinney said his team was still reviewing physical evidence and statements already gathered, and would "entertain the possibility" of interviewing the mine-rescue teams.

"Chances are that will take place down the road," he said.