According to the report, the launch occurred at about 8 a.m. (23:00 GMT Saturday) off Shinpo Port. No further details were provided, citing an ongoing analysis.
"While strengthening our monitoring and vigilance, our military has been closely coordinating with the United States to monitor additional signs of North Korea's provocations," the JCS told reporters in a text message.
Earlier this month, a spokesman for the North Korean National Defense Ministry said in a statement that Pyongyang had tested the still under-development "underwater nuclear weapon system Haeil-5-23" in the Sea of Japan in response to the joint three-day naval exercises by the United States, South Korea, and Japan involving a US nuclear carrier and other warships.