"Joint maritime exercises were staged again in the waters off Jeju Island for three days from Jan. 15 with the involvement of the U.S. nuclear carrier Carl Vinson and Aegis cruiser Princeton and warships of the Japanese maritime "Self-Defense Force" and the ROK navy," the spokesman said.
He said the drills further destabilized the regional situation and seriously threatened North Korea's security.
"In response to it, the Underwater Weapon System Institute under the DPRK Academy of Defense Science conducted an important test of its underwater nuclear weapon system "Haeil-5-23" under development in the East Sea of Korea," the spokesman said.