TOKYO - Japan's government has failed to create a revamped nuclear regulatory agency by the promised date, April 1, amid political infighting, raising questions about its commitment to bolstering oversight in the wake of last year's nuclear crisis.

Authorities have been accused of lax regulation and supervision of Japan's 54 nuclear reactors after a massive earthquake and tsunami led to a meltdown of three reactors at the Fukushima Dai-ichi plant in the world's worst nuclear accident since Chornobyl.

Prime Minister Yoshihiko Noda's Cabinet has endorsed a bill to create a more powerful and independent regulatory body similar to the U.S. Nuclear Regulatory Commission that would unify various nuclear safety and regulatory offices and be placed under the Environment Agency.

Currently, the main regulatory body, the Nuclear Industrial and Safety Agency, is under the control of the Ministry of Economy, Trade and Industry, which also promotes nuclear power in the resource-poor country.

But progress in setting up the new agency -- to be called the Nuclear Safety Regulation Agency -- has been slowed by disagreements between the ruling and opposition parties over how much independence it should have, as well by unrelated disputes such as a proposed sales tax hike.

"Obviously, having promoters and regulators under the same roof is not desirable, and we must unify related agencies that are scattered around," Environment Minister Goshi Hosono, who is also in charge of nuclear crisis management, told a parliamentary committee Monday.

He called the delay "regrettable."

The government hasn't set a new target date. Hosono has said that NISA and the Nuclear Safety Commission -- an advisory body of experts with no enforcement powers -- will continue to function for the time being. Some officials say the plan should wait until a parliament-appointed accident investigation panel releases its findings and recommendations in June.

Previous investigations into the Fukushima accident have found evidence of lax supervision by NISA, cozy relations with utilities and delays in upgrading safety measures.

On Monday, an NSC member told the same parliamentary committee that NISA repeatedly tried to block her commission's efforts in 2006 to upgrade nuclear accident management plans, saying it would cause unnecessary safety concerns and additional costs.

NSC was trying to extend the government's evacuation guidelines to 30 kilometres (18 miles) from 8-10 kilometres (5-6 miles) to match revisions by the U.N.'s International Atomic Energy Agency.

Shizuyo Kusumi, a radiation expert and one of five NSC members, said NISA was "very persistent" in its intervention.

"I now regret our revision was delayed," she said. "We were not fully independent and I hope the lessons will be used in a new agency."

In a memo dated April 24, 2006, NISA told the NSC, "We urge you to freeze this matter because it could trigger confusion and escalate public fear over nuclear safety."

Within days of the March 11, 2011, disaster, residents within 20 kilometres (12 miles) of the Fukushima plant had to be evacuated, but those living outside 10 kilometres had received no training.

If the revision had been in place before the accident, the 87,000 residents inside the 20-kilometre (12-mile) restricted area around the Fukushima plant "could have been evacuated more quickly and safely," Cabinet office official Hideaki Tsuzuki said.

The commission belatedly adopted a guideline in March - a full year after the crisis erupted - to require towns within 30 kilometres (18 miles) to have nuclear accident management plans.

NISA's current chief, Hiroyuki Fukano, said Monday that he regrets the agency was "not conscientious regarding international trends."

All but one Japan's 54 reactors are currently shut down, most of them for regular safety checks, and officials are desperately trying to avoid power shortages. The last remaining reactor is scheduled to go offline in early May.