Aso, though, reiterated his previous calls for greater debate on Japan's non-nuclear stance. He said the constitution’s pacifist clause does not prevent Japan from possessing nuclear bombs for defence purposes.
 
"Possession of minimum level of arms for defence is not prohibited under Article 9 of the constitution," he said. "Even nuclear weapons, if there are any that fall within that limit, they are not prohibited."
 
Aso has said that in light of North Korea's test, "it's only natural to discuss how we should cope with the changing environment around us".
 
However, Shinzo Abe, Japan's prime minister, has asserted several times since the North Korean test that Japan would not stray from its non-nuclear policy. He has refused to commence a formal review of the stance.
 
Nuclear energy accounts for about 30 per cent of Japan's energy production.