Japan should free up its "complex and rigid" reactor inspection regime, a global nuclear watchdog said Thursday, as the country restarts more atomic plants five years after the disaster at Fukushima.

A team of experts from the International Atomic Energy Agency (IAEA) said Tokyo must boost the number of trained nuclear officials and foster "distance" between them and the utilities they regulate.

The calls came as Japan readied to mark the March 11 anniversary of the 2011 earthquake and tsunami that caused disastrous meltdowns at the Fukushima nuclear power plant.

Japan's entire array of reactors was forced offline over the following months amid mounting public suspicion over nuclear technology and growing fears of radiation exposure.

The Japanese government says nuclear power is a necessity for the resource-poor country and a small number of reactors have gone back online since the crisis, with more expected to follow.

But the public has remained widely divided on the subject.

"What we found is the... framework for inspection is very, very complex and rigid," Philippe Jamet, a French Nuclear Safety Authority commissioner, who led the IAEA team, told reporters.

He said inspectors should be allowed to conduct surveys when and where they want.

"There is a comprehensive framework for inspections, but in Japan, it doesn't give enough freedom for inspectors to react immediately" when an abnormality occurs, he added.

Jamet also said that there should be "distance" between inspectors and utility companies, an apparent reference to the cosy ties and clubby nature of Japan's nuclear industry that critics said was a contributing factor to the magnitude of the disaster.

Japan invited the IAEA to conduct a 12-day review of its regulatory and policy issues.

On its website, the IAEA says it "works for the safe, secure and peaceful uses of nuclear science and technology."