N Korea Tests "Underwater Nuclear Weapon System" After US, S Korea Drills

North Korea said Friday that it had tested an "underwater nuclear weapon system" in response to joint naval exercises by Washington, Seoul and Tokyo, which involved a US nuclear-powered aircraft carrier.

The drills were "seriously threatening the security" of the North, so in response, Pyongyang "conducted an important test of its underwater nuclear weapon system 'Haeil-5-23' under development in the East Sea of Korea," according to a statement from the defence ministry carried by state news agency KCNA. 

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