"Our country has adopted an exclusively defensive security policy," he said, recalling that since the end of World War II Japan had never used force in an international or regional conflict.

But he warned that Tokyo still needed to maintain "sufficient deterrence ... to have other countries stop having a wrong idea that Japan will never react."

Missile tests carried out by North Korea in early July have prompted intensified debate in Japan about whether to deviate from the post-World War II constitution and develop a full-fledged military.

Japan has taken the hardest line against North Korea since it test-fired seven missiles including for the first time a Taepodong-2, which is believed to be able to hit Alaska or Hawaii but quickly crashed in the Sea of Japan (East Sea).

Earlier this month, South Korea accused Japan of planning a possible preemptive strike on the communist North after Japanese government ministers suggested there should be a debate on whether to develop such a capability.

A North Korean newspaper considered to be the mouthpiece of the ruling Workers Party also warned Japan that aggression would lead to its "destruction".

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