Holmes Mill, Ky. ? 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.