North Korea has offered a rare glimpse into a secretive facility to produce weapons-grade uranium as state media reported leader Kim Jong-un visited the area.
Friday's report said Kim called for stronger efforts to "exponentially" increase the number of his nuclear weapons.
It is unclear if the site is at the North's main Yongbyon nuclear complex, but it is the North's first public disclosure of a uranium-enrichment facility since it showed one at Yongbyon to visiting American scholars in 2010.
While the latest unveiling is likely an attempt to apply more pressure on the US and its allies, the images North Korea's media released of the area could provide outsiders with a valuable source of information for estimating the amount of nuclear ingredients that North Korea has produced.
During a visit to the Nuclear Weapons Institute and the production base of weapon-grade nuclear materials, Kim expressed "great satisfaction repeatedly over the wonderful technical force of the nuclear power field" held by North Korea, the official Korean Central News Agency (KCNA) reported.
KCNA said he went around the control room of the uranium enrichment base and a construction site that would expand its capacity for producing nuclear weapons.
State media photos showed Kim being briefed by scientists while walking along long lines of tall grey tubes, but KCNA did not say when he visited the facilities and where they are located.
KCNA said Kim stressed the need to further augment the number of centrifuges to "exponentially increase the nuclear weapons for self-defence", a goal he has repeatedly stated in recent years.
It said he ordered officials to push forward the introduction of a new-type centrifuge, which has reached its completion stage.
Kim said North Korea needs greater defence and pre-emptive attack capabilities because "anti-(North Korea) nuclear threats perpetrated by the US imperialists-led vassal forces have become more undisguised and crossed the red-line," KCNA said.
North Korea first showed a uranium enrichment site in Yongbyon to the outside world in November 2010, when it allowed a visiting delegation of Stanford University scholars led by nuclear physicist Siegfried Hecker to tour its centrifuges.
North Korean officials then reportedly told Mr Hecker that 2,000 centrifuges were already installed and running at Yongbyon.
Satellite images in recent years have indicated North Korea was expanding a uranium enrichment plant at its Yongbyon nuclear complex.
Nuclear weapons can be built using either highly enriched uranium or plutonium and North Korea has facilities to produce both at Yongbyon. It is not clear exactly how much weapons-grade plutonium or highly enriched uranium has been produced at Yongbyon and where North Korea stores it.
In 2018, Mr Hecker and Stanford University scholars estimated North Korea's highly enriched uranium inventory was 250 to 500 kilograms, sufficient for 25 to 30 nuclear devices.
Some US and South Korean experts speculate North Korea is covertly running at least one other uranium-enrichment plant.
In 2018, a top South Korean official told parliament that North Korea was estimated to have already manufactured up to 60 nuclear weapons. Estimates on how many nuclear bombs North Korea can add every year vary, ranging from six to as much as 18.
Since 2022, North Korea has sharply ramped up weapons testing activities to expand and modernise its arsenal of nuclear missiles targeting the US and South Korea.
Analysts say North Korea could perform nuclear test explosions or long-range missile tests ahead of the US presidential election in November with the intent to influence the outcome and increase its leverage in future dealings with the Americans.
North Korea conducted test launches of multiple short-range ballistic missiles on Thursday.
In an apparent reference to those launches, KCNA said Mr Kim had supervised test-firing of nuclear-capable 600mm multiple rockets to examine the performance of their new launch vehicles.
