North Korea says it tested “underwater nuclear weapon system”

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 U.S. 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 defense ministry carried by state news agency KCNA.  

This latest test comes less than a week after North Korea said it had tested a solid-fuel intermediate-range missile tipped with a hypersonic warhead, The Associated Press reported.

This story will be updated.