Yoon Suk-yeol calls for "complete denuclearisation" of North Korea, saying in his first speech as president that Pyongyang's weapons programmes were a threat to global security.
Yoon Suk-yeol has been sworn in as South Korean president in a huge ceremony at Seoul's National Assembly, taking office at a time of high tensions with the nuclear-armed North.
"I solemnly swear before the people that I will faithfully perform the duties of the president," said Yoon, a hawkish conservative, on Tuesday.
Yoon said in his first speech as president that South Korea was prepared to present an "audacious plan" to strengthen North Korea's economy if it embarks on a process to complete denuclearisation.
"While North Korea's nuclear weapon programmes 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.
Yoon, 61, takes office at a time of high tensions on the Korean peninsula, with an increasingly belligerent North Korea conducting a record 15 weapons tests since January, including two launches last week.
His conservative administration looks set to usher in a more muscular foreign policy for the world's 10th-largest economy after the dovish approach pursued by outgoing President Moon Jae-in during his five years in office.
After winning a tight race in March by the narrowest margin, the new president vowed to "sternly deal" with the threat posed by Kim Jong-un's regime, while saying he would leave the door to dialogue open.
Under Moon, Seoul pursued a policy of engagement with North Korea, brokering summits between Kim Jong-un and then-US president Donald Trump. But talks collapsed in 2019 and diplomacy has stalled since.
'Symbol of imperial power'
Moon remains personally popular, but public frustration with his administration helped sweep his opponent Yoon to power.
But it won't be an easy ride: Yoon is taking office with some of the lowest approval ratings –– about 41 percent, according to a recent Gallup poll –– of any democratically elected South Korean president.
His plan to relocate the presidential office from the decades-old Blue House has soured public sentiment, as many view the costly move as unnecessary.
But Yoon has blasted the Blue House as a "symbol of imperial power", claiming the relocation will ensure a more democratic presidency.
Around 40,000 people were invited to attend the inauguration ceremony, which is by far the most expensive event of its kind.
US President Joe Biden designated Douglas Emhoff, husband of US Vice President Kamala Harris, to lead an eight-member presidential delegation, the White House said in a statement last week.
Japan and China have also sent high-level representatives, with Yoon saying he wants to mend sometimes fractious relations with regional powers.