South Korea threatened the Democratic People's Republic of Korea, saying if the latter were to use nuclear weapons, "the North Korean regime will face its end."

Seoul and Washington have "made clear" previously that "any nuclear attack on the alliance will face an immediate overwhelming and decisive response," the South Korean Ministry of National Defense said in a statement.

These threats follow the US deployment of a nuclear-capable submarine in Korean waters, which led the Pyongyang Defense Ministry to assert 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 the DPRK law."

The law that the Ministry referenced in the above statement is a set of guidelines, approved in 2022, outlining events in which the use of nuclear weapons would be justified as an act of preemptive defense.

Read more: US nuclear ballistic missile sub arrives in S. Korea, first since 1980s

South Korea claims that the arrival of the USS Kentucky (SSBN 737) in Busan port is only a defensive measure, however, the submarine carries ballistic missiles that could be armed with nuclear warheads, marking another form of escalation in the Korean Peninsula.

The nuclear-powered submarine's docking at Busan port was preceded by the docking of USS Michigan, a nuclear-powered submarine that carries cruise missiles. These visits have been long expected since April when South Korean President Yoon Suk Yeol met with US President Joe Biden.

The allies held their first Nuclear Consultative Group meeting in the South Korean capital on Tuesday to enhance their joint action in case nuclear war breaks out.

Washington and Seoul also held their first Nuclear Consultative Group meeting in Seoul Tuesday to improve their joint response to any alleged nuclear attack by the DPRK.

They have also followed large-scale joint military drills, in which the two countries simulated bombing campaigns and advancements into DPRK territories using state-of-the-art military equipment.

Stranded US soldier

On Wednesday, news broke out that a US soldier crossed the demarcation line to the DPRK. Private Travis King "willfully and without authorization" crossed over during a civilian tour of the Joint Security Area, which is a demilitarized zone that has separated Korea since the end of the Korean War in 1953.

In a statement, US Forces Korea spokesperson Col. Isaac Taylor said, “We believe he is currently in [Democratic People’s Republic of Korea] custody and are working with our [Korean People’s Army] counterparts to resolve this incident."

King, a cavalry scout who joined the military in January 2021, was assigned to the 6th Squadron, 1st Cavalry Regiment, 1st Brigade Combat Team, 1st Armored Division out of Fort Bliss, Texas, at the time of his duty in South Korea, per Army spokesperson Bryce Dubee.

King is the first US soldier to cross into the DPRK since 1982. His mother, Claudine Gates, expressed to ABC News that she was "shocked" to hear the news.

"I can’t see Travis doing anything like that," she said, explaining that she spoke to her son several days ago, and he told her that he’d be returning to his base in Fort Bliss.

Read more: The US soldier that crossed to the DPRK