SEOUL -- The Democratic People's Republic of Korea (DPRK) conducted a test of its underwater nuclear weapon system in the eastern waters, the official Korean Central News Agency (KCNA) reported Friday.

A spokesman for the Ministry of National Defence of the DPRK announced the move in a press statement, said the report.

The DPRK tested the "Haeil-5-23," an underwater nuclear weapon system under development, in response to the joint maritime exercises by the United States, Japan and the Republic of Korea earlier this week, the statement said.

It accused the three-day trilateral naval drill as an act of destabilizing the regional situation and seriously threatening the security of the DPRK.

The underwater nuke-based countering posture of the DPRK armed forces, it said, is being further rounded off and the country will continue its maritime and underwater actions to deter the hostile military maneuvers of the navies of the United States and its allies.

It "strongly denounces the US and its followers for their reckless acts of seriously threatening the security of the DPRK from the outset of the year and sternly warn them of the catastrophic consequences."

The ROK, the United States and Japan have jointly conducted naval drills in southeastern waters off Jeju Island involving warships of the three nations, including the US nuclear-powered aircraft carrier USS Carl Vinson, from Monday to Wednesday, ROK's Yonhap news agency reported, citing a Wednesday press release by the country's Joint Chiefs of Staff.