South Korea's new president, Yoon Suk Yeol, said on Tuesday that North Korea's weapons programmes pose a threat but that he is ready to provide an "audacious" economic plan if the North is committed to denuclearisation.

Yoon gave the remarks in his inauguration speech after being sworn in at a ceremony in front of parliament in Seoul. He won a tight election in March as the standard bearer of the main conservative People Power Party, less than a year after entering politics following a 26-year career as a prosecutor.

Yoon, 61, will face two major problems as he takes office: a belligerent North Korea testing new weapons and inflation threatening to undermine an economic recovery from two years of Covid-19 gloom.

He has signalled a tougher line on North Korea, warning of a preemptive strike if there is a sign of an imminent attack and vowing to strengthen the South's deterrent capability. But his speech was seen as focused more on his willingness to reopen stalled denuclearisation talks with Pyongyang.

"While North Korea's nuclear weapon programs are a threat not only to our security and that of Northeast Asia, the door to dialogue will remain open so that we can peacefully resolve this threat," Yoon said.

"If North Korea genuinely embarks on a process to complete denuclearisation, we are prepared to work with the international community to present an audacious plan that will vastly strengthen North Korea's economy and improve the quality of life for its people," he added.

Yoon did not elaborate on his plan to re-engage or provide economic incentives to the North. But his national security adviser, Kim Sung-han, said during the election campaign that the Yoon government would devise a roadmap in early days in which Pyongyang could quickly earn sanctions relief or economic aid in exchange for denuclearisation measures.

Yoon could face a security crisis if North Korea carries out its first nuclear test in five years, as US and South Korean officials warned, after it broke a 2017 moratorium on long-range missile testing in March.

Yoon won the election on a platform of fighting corruption and creating a more level economic playing field amid deepening public frustration with inequality and housing prices, as well as simmering gender and generational rivalry. (Reuters)