The defense ministry has hit back against North Korea’s threat of nuclear retaliation over a port call in South Korea by a U.S. nuclear-capable strategic submarine this week.

The ministry said on Friday that the Nuclear Consultative Group(NCG) meeting of South Korea and the U.S. and the deployment of a U.S. nuclear-capable strategic submarine to Busan were legitimate defense measures against the continued threats from North Korea’s nuclear weapons and missiles.

Criticizing the North’s nuclear and missile provocations as clear violations of the UN Security Council resolutions, the ministry denounced the regime's adoption of a law allowing unlawful preemptive nuclear strikes and related exercises as well as repeated nuclear threats against the South Korea-U.S. alliance.

It then warned that any North Korean nuclear attack against the alliance will face an immediate, overwhelming and decisive response.

The warning came a day after Pyongyang's defense minister, Kang Sun-nam, threatened possible nuclear retaliation over the deployment of the U.S. Navy's Ohio-class ballistic missile submarine, the USS Kentucky, to South Korea.

The submarine arrived in the southeastern port city of Busan on Tuesday, coinciding with the first session of the NCG.