"When looking back on the accident, the problem was that preparations were not made in advance," states the report, prepared by a nuclear reform task force.
That stance represents an about-face for Tepco, which has maintained that it had done its best to prevent an accident from occurring.
"There was a worry that if the company were to implement a severe-accident response plan, it would spur anxiety throughout the country and in the community where the plant is sited, and lend momentum to the anti-nuclear movement,'' the committee said in the report issued Friday.
Tepco announced the third-party committee Sept. 11 to oversee the reform of its nuclear power division.
The report said Tepco admitted that some suggested safety improvements, such as using multiple power sources and cooling systems, would have involved closing the plant temporarily, thus adding to its costs.
"It is very clear that mistakes were made,'' said Dale Klein, committee member and former chairman of the U.S. Nuclear Regulatory Commission, at a news conference following the committee's first meeting on Friday, The Wall Street Journal reports. "The committee's goal is to ensure that Tepco develops practices and procedures so an accident like this will never happen again.''
While Tepco's acknowledgement that it has made mistakes is likely to have far-reaching impacts on issues including lawsuits related to the Fukushima disaster, the level of Tepco's liability is still not clear. A Tepco spokesman said the company hasn't said it is liable for the accident, nor has it denied liability, the Journal reports.
"Tepco has changed its position 180 degrees,'' Yui Kimura, a plaintiff in a shareholder suit against Tepco executives over the accident, was quoted as saying by the Journal. "We want to know whether this represents a real change of heart.''
While operations at all of Tepco's 13 nuclear reactors are now suspended, the company plans to reactivate the seven reactors at its Kazhiwazaki-Kariwa nuclear power plant in Niigata Prefecture, a key power generation facility, in phases beginning in spring 2013.
Speaking at the Asahi World Environmental Forum 2012 in Tokyo Monday, Japanese Prime Minister Yoshihiko Noda said that the country's new energy policy set last month aims to phase out nuclear power by the end of the 2030s.
"Wishes are shared by many in the Japanese public to become a society that does not depend on nuclear energy," Noda said.
Prior to the Fukushima crisis, nuclear power provided 30 percent of Japan's electricity.