North Korea has threatened possible nuclear retaliation over a port call in South Korea by a U.S. nuclear-capable strategic submarine this week.

North Korean Defense Minister Kang Sun-nam issued the warning in a statement carried by the North’s official Korean Central News Agency on Thursday.

In the release, Kang reminded the U.S. military of the fact that the increasing visibility of the deployment of the strategic nuclear submarine and other strategic assets may fall under the conditions of the use of nuclear weapons specified in North Korean law on nuclear force policy.

The defense chief added that the North's nuclear policy allows for the execution of necessary procedures in cases where a nuclear attack is launched against the country or is judged to be imminent.

Kang also said that the U.S. military should realize that its nuclear assets have entered “extremely dangerous waters” with the port call of an Ohio-class ballistic-missile submarine in Busan, which he claimed was the first time such strategic nuclear weapons have been deployed on the peninsula in some 40 years.

The visit by the USS Kentucky on Tuesday coincided with the first session of the Nuclear Consultative Group established by South Korea and the U.S.

North Korea also warned that the use of military force against Pyongyang would be “the most miserable choice” for South Korea and the U.S.

[Photo : YONHAP News]