North Korea conducts test of underwater nuclear weapon system: KCNA

North Korea conducted a test of its underwater nuclear weapon system, according to the state-run outlet KCNA.

North Korea conducted a test of its underwater nuclear weapon system in response to the United States, Japan and South Korea's "joint military exercises," state-run media Korean Central News Agency said on Friday.

The "joint maritime exercises" conducted by the three countries, which took place in the waters around Jeju Island, have "become a cause of further destabilization of the regional situation" and a "serious threat" to the security of North Korea, according to an unnamed spokesperson at the North Korean Ministry of Defense, per KCNA.

As a countermeasure to the "serious threat," North Korea tested its "Haeil 5-23" system, which has been under development in the waters of the East Sea, according to the KCNA.

It's unclear how long the system has been under development.