The International Atomic Energy Agency says the Japanese government's complicated organizational structure caused it to respond more slowly than it should have to the nuclear accident at Fukushima.

The agency advises Japan to streamline its regulatory structure so it can hand down decisions more quickly.

IAEA experts who visited Japan late last month said the country underestimated the size of the tsunami that hit the Fukushima plant, and that safety measures must be bolstered to deal with natural disasters.