CHARLESTON (AP) — Sen. Jay Rockefeller has asked the Obama administration to do a better job keeping the families of the Upper Big Branch mine explosion victims informed about the government's investigation of the tragedy.

Families of the 29 miners killed in the April 5 explosion haven't been briefed by the Mine Safety and Health Administration since September, Rockefeller said in a letter sent to U.S. Labor Secretary Hilda Solis.

"Three months is too long for these families to wait for information," Rockefeller wrote. "I request that MSHA meet with these families as soon as possible, and that you provide me with the expected date that this briefing will occur. Further, I would also request an update on the status of MSHA's investigation, including when we can expect the investigation to be completed."

MSHA has not set a target date and still has investigators working inside the Raleigh County mine. West Virginia investigators have targeted next summer to complete their work. The U.S. Department of Justice has not commented on the progress of its criminal investigation.

Mine owner Massey Energy Co. has suggested the explosion was caused by an unexpected inundation of natural gas that rushed into the mine so quickly that it overwhelmed safeguards. MSHA has largely dismissed the company's version of events.

The Labor Department said it intends to meet with the Upper Big Branch families after the holidays.

"Our response to Senator Rockefeller's letter will provide additional details, including an outline of our ongoing efforts to keep the victims' families up to date on the status of the investigation," the agency said in a statement.