SEOUL, South Korea, Sept 25, (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 US 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.

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. 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.