Results of the probe were expected in mid-September. However, the team said on Sept 21 that many problems have yet to be analyzed due to technical and management issues.
"Much basic work has been done and important basic data and test materials have been obtained," Xinhua News Agency quoted the investigation team as saying. "But the accident investigation report still needs some time to be put together."
The team will "take a rigorous, conscientiously responsible attitude and continue to keep a firm grasp on the job at hand ... and will not let slip any uncertain points".
The results will be released to the public "in a timely manner", Xinhua reported, without giving a timeframe.
The State Council established the panel in late July, shortly after a crash involving two bullet trains in East China's
In the past two months, experts have held 200 meetings and collected more than 1,300 documents to date, as well as obtained fundamental data and materials, according to an official statement from the probe panel.
In a speech, Premier Wen Jiabao vowed that the investigation would be thorough and transparent, and that several senior railway officials had been fired.
A Chinese railway research institute also took responsibility for a flaw in signaling equipment that led to the accident and the authorities promised a full review of safety procedures.