TOKYO — From inspectors’ abandoning of the Fukushima Daiichi nuclear power plant as it succumbed to disaster to a delay in disclosing radiation leaks, Japan’s response to the nuclear accident caused by the March tsunami fell tragically short, a government-appointed investigative panel said on Monday.

The failures, which the panel said worsened the extent of the disaster, were outlined in a 500-page interim report detailing Japan’s response to the calamitous events that unfolded at the Fukushima plant after the March 11 earthquake and tsunami knocked out all of the site’s power.

Three of the plant’s six reactors overheated and their fuel melted down, and hydrogen explosions blew the tops off three reactor buildings, leading to a major leak of radiation at levels not seen since Chernobyl in 1986.

The panel attacked the use of the term “soteigai,” or “unforeseen,” that plant and government officials used both to describe the unprecedented scale of the disaster and to explain why they were unable to stop it. Running a nuclear power plant inherently required officials to foresee the unforeseen, said the panel’s chairman, Yotaro Hatamura, a professor emeritus in engineering at the University of Tokyo.