The US has repeatedly promised to use all its military capabilities to protect South Korea if it is attacked by North Korea North Korea has argued it was forced to pursue nuclear weapons to deal with US-led nuclear threats SEOUL, South Korea: North Korea threatened Saturday to boost its nuclear fighting capability and make the US and South Korea pay “an unimaginably harsh price” as it slammed its rivals’ new defense guidelines that it says reveal an intention to invade the North. On Thursday, President Joe Biden and South Korean President Yoon Suk Yeol authorized the signing of joint nuclear deterrence guidelines as part of efforts to enhance their capabilities to cope with North Korea’s growing nuclear arsenal. The guidelines were adopted a year after the two countries established a consultation body to bolster information-sharing on nuclear operations and discuss how to integrate US nuclear weapons and South Korean conventional weapons in contingencies. In a statement carried by state media, North Korea’s Defense Ministry said the US-South Korea guidelines betrayed “their sinister intention to step up their preparations for a nuclear war against” North Korea. The statement said its enemies’ escalating nuclear threats urgently require North Korea to further improve its nuclear deterrent readiness and add unspecified “important elements to the composition of the deterrent.” It said the US and South Korea will “pay an unimaginably harsh price” if they fail to stop provocative acts. Details of the US-South Korean guidelines weren’t available, but experts say they are largely about how the two countries would integrate US nuclear weapons and South Korean conventional weapons to respond to various potential contingencies caused by North Korean attacks and provocations. Experts say the US and South Korea are expected to map out detailed concept and operation plans based on the guidelines and review them via bilateral military exercises. The guidelines are the first of kind between the allies. The US has repeatedly promised to use all its military capabilities to protect South Korea if it is attacked by North Korea, but many experts in South Korea believe the US lacks plans on how it would implement its extended deterrence to its ally. South Korea has no nuclear weapons. North Korea has argued it was forced to pursue nuclear weapons to deal with US-led nuclear threats. US and South Korean officials have steadfastly said they have no intention of attacking North Korea. Concerns about North Korea’s nuclear program have grown in recent years as the North has performed a slew of provocative missile tests and openly threatened to use nuclear weapons preemptively in potential conflicts with its adversaries.