This photo, provided by the Defense Daily on Wednesday, shows the USS Kentucky nuclear ballistic missile submarine at a key naval base in Busan, 320 kilometers southeast of Seoul. (Yonhap)

North Korea's defense chief warned Thursday a US nuclear-capable strategic submarine's port visit to South Korea this week may fall under the legal conditions for his country's use of nuclear weapons.

Defense Minister Kang Sun-nam made the remarks, issuing an anticipated criticism of the visit here by the USS Kentucky, an 18,750-ton Ohio-class ballistic missile submarine (SSBN), and the recent inaugural meeting of the Nuclear Consultative Group (NCG) between South Korea and the United States.

"I remind the US military of the fact that the ever-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 DPRK law on nuclear force policy," he said in a press statement carried by the North's official Korean Central News Agency.

DPRK stands for the North's official name, the Democratic People's Republic of Korea.

Kang pointed out that the North's nuclear doctrine allows for the execution of necessary procedures in cases where a nuclear attack is launched against it or it is judged that the use of nuclear weapons against it is imminent.

"The US military side should realize that its nuclear assets have entered extremely dangerous waters," he said.

The USS Kentucky arrived in the southeastern port city of Busan on Tuesday, marking the first US SSBN arrival here since 1981. Its arrival coincided with the first NCG session.

The US pledged to enhance the "regular visibility" of its high-profile military assets, including SSBNs, in the Washington Declaration that Presidents Yoon Suk Yeol and Joe Biden issued during their summit in April.

In the declaration, the two sides announced the creation of the NCG aimed at enhancing America's extended deterrence commitment to using the full range of its military capabilities, including nuclear, to defend its ally. (Yonhap)