Seoul, Jan 31 : US Defence Secretary Lloyd Austin on Tuesday highlighted America's "ironclad" and "unwavering" security commitment to South Korea, as some raise doubts about Washington's "extended deterrence" commitment for the key ally amid evolving North Korean threats. He said there would be more frequent deployments of such high-profile US strategic assets as advanced stealth jets and aircraft carriers to Korea, speaking at a joint press conference with his South Korean counterpart, Lee Jong-sup, following bilateral talks in Seoul, Yonhap News Agency reported. "Our commitment to the defence of the ROK remains ironclad, and the US stands firm in its extended deterrence commitment," he said, referring to South Korea by its official name, the Republic of Korea. "That includes the full range of US defence capabilities, including our conventional, nuclear and missile defense capabilities. Now, we have 28,500 uniformed personnel in South Korea... This shows our unwavering commitment," he added. His remarks came after North Korean leader Kim Jong-un publicly called for an "exponential" increase in his country's nuclear arsenal and named the South an "undoubted" enemy at a December ruling party meeting. Kim's rhetoric has added to a debate over whether the South should develop its own nuclear weapons or request the US' redeployment of tactical nuclear arms to the Korean Peninsula. In an apparent message to both Koreas, Austin stressed the goal of the "denuclearisation of the Korean Peninsula." "The US and the ROK are committed to the denuclearisation of the Korean Peninsula, and we've long been that way," he said. He added Washington's repetitive mantra of the "ironclad" security commitment is "not just a slogan." "It is what we're all about," he said. As a vivid example of the US commitment, the Pentagon chief recalled last year's deployment here of America's fifth-generation fighter jets, like F-22 and F-35 radar-evading fighter jets, and of an aircraft strike group. He also mentioned the allies' plan to hold table-top exercises to sharpen deterrence. "We want to make sure that no stone is left unturned," he said. Lee and Austin had their last bilateral in-person talks at the annual Security Consultative Meeting at the Pentagon last November. The Pentagon chief arrived here on Monday on a regional swing that will also take him to the Philippines. /IANS