Facing widespread criticism for its handling of the crisis at the Fukushima Daiichi plant, the Japanese government on Tuesday announced its intention to create an independent nuclear agency, breaking up the ministry that both promotes and regulates atomic energy.

The decision to separate the regulator (the Nuclear and Industrial Safety Agency, or NISA) from the promoter (the Ministry of Economy, Trade and Industry, or METI) came as part of a government report that calls for several major overhauls in the way Japan operates its nuclear plants and provides information about the ongoing crisis after the earthquake and tsunami in March. Previously, NISA was a subdivision of METI, an arrangement that critics say contributed to lax oversight of nuclear safety in Japan.

The report, to be submitted this month to the International Atomic Energy Agency, also serves as a reminder of the challenges at the disaster-stricken facility. In it, Japan cites the “possibility” that melted fuel has penetrated the reactor pressure vessels in units 1, 2 and 3 and dropped on to the floors of the primary containment vessel. That acknowledgment came a day after the government doubled its estimate of the radiation released so far during the crisis.

The report is at once a pointed self-critique and a pledge to learn from mistakes. Many of its admissions are familiar, echoing assessments by international agencies and outside experts. They include acknowledgments that Fukushima Daiichi was unprepared for a tsunami and that the government was too slow to provide information on radiation to people in the disaster zone.

But the report also lends insight into the jumbled initial response, which was characterized by poor communication among the government and the plant operator, Tokyo Electric Power, as well as government agencies. It was unclear, the report says, exactly who had ultimate authority for nuclear safety. NISA is a regulator, but it was tucked within METI. And Japan’s Nuclear Safety Commission was responsible for part of METI. Local governments were in charge of environmental monitoring.

“This is why it was not clear who has the primary responsibility for ensuring citizens’ safety in an emergency,” the report says. “Also, we cannot deny that the existing organizations and structures made mobilization of capabilities difficult to promptly respond to such a large-scale nuclear accident.”

As the disaster unfolded, Japanese authorities relied on computer models and uncertain data while trying to assess the full scope of the damage to the reactor cores. Even now, it will probably be years before guesses about units 1, 2 and 3 turn into facts. But the government’s admission Tuesday of a possible melt-through reaffirmed assumptions held by outside scientists.

“It’s much like the Japanese government conceding that gravity is a possibility,” David Lochbaum, an independent nuclear power expert, wrote in an e-mail. “Studies for decades have consistently concluded that a reactor core without cooling and makeup will overheat, melt, slump to the bottom of the reactor vessel, and burn through the vessel wall and drop on to the drywell floor.”

Goshi Hosono, the lawmaker in charge of the latest report, said that the government often found itself torn over whether to release unconfirmed — and constantly changing — information to the public. Too often, he said, officials preferred to wait, opening themselves to accusations that they were hiding information.

On March 18, for instance, Japan raised its assessment of the Fukushima accident to a Level 5, using the International Nuclear and Radiological Event Scale. On April 12, it revised that assessment, giving Fukushima a Level 7 rating — on par with Chernobyl.

The government should have been more forthcoming in March, Hosono said during an interview in his office.

“We could have — and should have — told the public even then [on March 18] that there was the possibility of a full meltdown and a level 7 event,” Hosono said.

Special correspondent Akiko Yamamoto contributed to this report.