By Anadolu Agency 

ISTANBUL (AA) - North Korea on Friday said it conducted a test of an underwater nuclear weapon system in response to joint military drills conducted by the US, South Korea, and Japan.

“We will never tolerate the reckless military confrontation hysteria,” the Defense Ministry said, referring to three-day maritime drills held off South Korea's Jeju Island which concluded Wednesday.

It said the three allies were “getting frantic” by holding “provocative military exercises from the outset of the year.”

As a response, the ministry said it conducted “an important test of its underwater nuclear weapon system ‘Haeil-5-23’ under development” in the East Sea.

The trilateral maritime exercise by Seoul, Washington, and Tokyo included the US nuclear carrier USS Carl Vinson and the Aegis-guided missile cruiser USS Princeton.

Pyongyang said the joint drill “constituted a cause of further destabilizing the regional situation, and they are an act of seriously threatening the security” of North Korea.

“We strongly denounce the US and its followers for their reckless acts … and sternly warn them of the catastrophic consequences to be entailed by them,” said the ministry, referring to Seoul and Tokyo.

The ministry said its underwater nuke-based “countering posture is being further rounded off and its various maritime and underwater responsive actions will continue to deter the hostile military maneuvers of the navies of the US and its allies.”

Meanwhile, Seoul called for an "international response" to Pyongyang's "evolving military threats" during a meeting of NATO in Brussels.

South Korean military representative Lt. Gen. Hwang You-sung attended the meeting of top NATO military officials along with those from Australia, Japan, and New Zealand.