His trip highlighting the country's growing nuclear arsenal came as Pyongyang has been ramping up its show of force around US President Donald Trump's return to office with a resumption of missile tests, which South Korea said were partly aimed at enticing Trump's attention.
Kim praised scientists and other workers there for achieving "remarkable successes" and "amazing production results" in their work last year as he was briefed about the process for producing weapons-grade nuclear materials and their plan for 2025 and beyond, state media KCNA reported on Wednesday.
Kim called for further success in producing weapons-grade nuclear materials this year and strengthening the country's nuclear forces.
"This year is a crucial year as it is an important watershed in which we should carry out the tasks in the important period in the course of implementing the line of bolstering up the nuclear forces," Kim said, according to KCNA.
North Korea faces "the world's most unstable security situation" due to a longstanding confrontation with "the most vicious hostile countries," which makes it indispensable for the country to boost its nuclear capability, he added.
Pyongyang has long argued that its nuclear arsenal is aimed at fending off threats from Washington and its allies, which fought the North during the 1950-53 Korean War.
Analysts estimate North Korea may have produced enough fissile material to build up to 90 nuclear warheads.
Seoul's National Intelligence Service has said the North's recent display of force was in part intended to "show off its US deterrent assets and draw Trump's attention" after vowing "the toughest anti-US counteraction" at a key year-end policy meeting last month.
Trump, who held unprecedented summits with Kim during his first term and has touted their personal rapport, said last week he would "reach out to him again."
On January 20, the day of his inauguration, Trump described North Korea as a "nuclear power," as had his now Defence Secretary Pete Hegseth at his Senate confirmation hearing, raising questions about whether Washington would seek arms reduction talks rather than denuclearisation negotiations.
The White House did not immediately respond to a request for comment, but a person familiar with the matter told Reuters that Trump would continue to pursue a denuclearisation of the Korean Peninsula.
South Korea's Yonhap news agency reported on Wednesday that Trump woul pursue North Korea's "complete denuclearisation", citing National Security Council spokesman Brian Hughes.Â
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