Pyongyang also accused US spy planes of violating its airspace and warns such aircraft may be shot down.

In a statement carried by the Korean Central News Agency (KCNA) on Monday, a spokesperson for the North Korean defence ministry said Washington’s plan – agreed to by the leaders of the US and South Korea during an April summit – would introduce US strategic nuclear weapons to the Korean peninsula for the first time since 1981.

“This is a very dangerous situation as it will bring the regional military tension to a more critical state and may incite the worst crisis of nuclear conflict in practice,” the unnamed spokesperson said.

The US plan is blatant nuclear blackmail against North Korea as well as regional countries and presents a grave threat to peace, the KCNA said.

“It is up to future US actions whether an extreme situation arises in the Korean peninsula region that nobody wants, and the United States will be held fully responsible if any unexpected situation occurs,” it said.

US President Joe Biden and his South Korean counterpart, Yoon Suk-yeol, agreed in Washington in April that a US Navy nuclear-armed ballistic missile submarine will visit South Korea, though no timetable has been given for such a visit.

The visit is part of an effort to boost the deployment of US strategic assets to more effectively respond to North Korea’s accelerating nuclear and ballistic missiles programme.

A US nuclear-powered cruise missile submarine arrived at the port of Busan in South Korea last month, while in June, a US B-52 strategic bomber took part in air military drills with South Korea in a show of force following North Korea’s failed launch of a spy satellite.

Pyongyang said the US move to sail nuclear submarines has created a “very dangerous situation that makes it impossible for us not to realistically accept the worst-case scenario of a nuclear confrontation”.

It also claimed US reconnaissance planes recently violated its air space near the east coast, warning that “there is no guarantee that a shocking incident where a US air force strategic reconnaissance plane is shot down over the East Sea will not happen”.

The statement cited past incidents of North Korea shooting down or intercepting US aircraft at the border with South Korea and off the coast.

The North Korean threats came as Yoon prepared to attend an annual NATO summit being held this year in Vilnius, Lithuania, on Tuesday and Wednesday.

It marks the second consecutive year the South Korean leader will take part in the summit, underscoring his push to deepen ties with the world’s biggest military alliance.

Ahead of his departure, Yoon, in a statement to The Associated Press news agency, said it was time for the international community to show that its “determination to deter North Korea’s nuclear weapons programme is stronger than North Korea’s desire to develop nuclear weapons”.

Yoon said South Korea will stress at the NATO meeting the importance of international cooperation against “North Korea’s illegal acts”.

He also said a new NATO-South Korean document will take effect at the summit to institutionalise cooperation in 11 areas, including non-proliferation and cybersecurity.

Yoon’s discussion of North Korea with NATO leaders could trigger a backlash from Pyongyang, which has already called increasing cooperation between NATO and US allies in Asia a process to create an “Asian version of NATO” that it claimed would increase regional animosities.

North Korea argues its weapons-testing spree is an effort to boost defence in the face of expanded South Korean-US military drills that it views as rehearsals for invasion. Yoon says he wants to opt for peace through strength but remains open to dialogue with North Korea.

“Peace is never as certain and reliable as when it is backed by powerful force and deterrence,” Yoon added. “Strong international sanctions against North Korea have the effect of preventing the advancement of its nuclear and missile capabilities.”

Yoon will attend the NATO summit along with the leaders of Japan, Australia and New Zealand, a sign of strengthening ties between NATO and nations in the Asia-Pacific region. The four countries were also invited to last year’s summit.