CHOLMES MILL, Ky. (AP) – Federal officials have yet to enter an eastern Kentucky mine to begin investigating the cause of an underground explosion that killed five miners. The U.S. Mine Safety and Health Administration said Saturday the mine won’t be safe for investigators until its owner repairs some walled-off areas.

But state officials entered the Darby Mine No. 1 Thursday after checking gas levels and air quality.

MSHA spokesman Dirk Fillpot declined to comment on the state’s decision to enter the mine. He said he did not have a time frame for when the federal investigation would start.

“Because of conditions observed after the explosion in this mine, MSHA is requiring the operator to build new seals as a precaution to ensure that the mine is safe for investigators,” he said.

State inspectors from the Kentucky Office of Mine Safety and Licensing began mapping the inside area this week to determine what caused the explosion.

“Our guys felt the mine was safe to work in or else they wouldn’t have gone in,” said Chuck Wolfe, a spokesman for the Kentucky Environmental and Public Protection Cabinet.

Before entering, investigators worried about carbon monoxide and methane gas levels in the mine. Preliminary autopsy reports said three of the miners died of carbon monoxide poisoning.

The mine has been closed since the explosion.

AP-ES-05-27-06 1722EDT