SEOUL, South Korea (AP) -- A top South Korean official said Thursday that North Korea is operating a total of four uranium enrichment facilities, adding to outside assessments that it has multiple covert atomic plants along with the widely known site near the capital of Pyongyang.
The North's leader Kim Jong Un has called for a rapid expansion of his country's nuclear weapons program and recently said he would never make the arms a negotiating point in response to overtures by U.S. President Donald Trump.
The South's Unification Minister Chung Dong-young said uranium enrichment centrifuges at the four facilities -- which would include the known site at Yongbyon, about 100 kilometers (60 miles) north of Pyongyang -- are running everyday and stressed the urgency to stop the North's nuclear program.
Chung did not elaborate further on the location of the other, undeclared nuclear sites. He spoke about the North with local reporters, according to his ministry.
A nuclear stockpile
Chung cited an assessment that the North possesses 2,000 kilograms (about 4,400 pounds) of highly enriched uranium. He first said that was based on intelligence but the ministry later clarified it was attributed to civilian experts.
If confirmed, the amount would also signal a sharp increase in North Korea's stockpile of nuclear material.
In 2018, Stanford University scholars, including nuclear physicist Siegfried Hecker who had previously visited the Yongbyon complex, said the North had about 250 to 500 kilograms (550 to 1,100 pounds) of highly enriched uranium, sufficient for 25 to 30 nuclear devices.
Nuclear weapons can be built using either highly enriched uranium or plutonium, and North Korea has facilities to produce both at Yongbyon. Last year, North Korea released photographs of what it said was a uranium enrichment facility, the first such disclosure since it showed the one at Yongbyon to Hecker and others in 2010.
The location and other details of the facility in the photographs remain unknown.
Foreign experts believe North Korea has built additional uranium-enrichment sites as Kim has been pushing hard to expand his nuclear arsenal.
A plutonium plant is typically large and generates much heat, making it easier for outsiders to detect than a uranium enrichment plant, which is more compact and can be easily hidden from satellite cameras. Centrifuges to enrich uranium can be clandestinely operated underground.
North's atomic bombs
It's almost impossible to independently confirm how many nuclear weapons North Korea has manufactured, based on nuclear fissile materials it has produced at Yongbyon and elsewhere.
In 2018, a top South Korean official told parliament that North Korea was estimated to have already manufactured 20-60 nuclear weapons, but some experts say the North likely has more than 100. Estimates of how many nuclear bombs North Korea can add to its arsenal every year vary, ranging from six to as many as 18.
International diplomacy on ending North Korea's nuclear program has stalled since 2019, when high-stakes summitry between Kim and Trump fell apart without any agreement.
At the time, Kim offered to dismantle the Yongbyon complex if he won extensive sanctions relief. But the American side rejected his proposal, because it would be a limited denuclearization step that would leave North Korea's other, already built nuclear weapons and nuclear facilities intact.
Kim has since shunned any diplomacy with the U.S. and South Korea and focused on running weapons tests and perfecting nuclear missiles that target his rivals.
Since returning to office, Trump has repeatedly expressed hopes of restarting talks with Kim. Earlier this week, Kim said he still has good memories of Trump but urged the U.S. to drop its demand that the North surrender its nuclear arms as a precondition for resuming long-stalled diplomacy.
Analysts assess that Kim would likely perceive an enlarged nuclear arsenal as a source of greater leverage in potential talks with the U.S.
They say that in any potential negotiations, Kim would again seek to win sweeping sanctions relief and improved ties with the U.S. in return for a partial surrender of his nuclear and missile programs.