North Korean leader Kim Jong Un has called for his nuclear scientists to increase production of weapons-grade material to make bombs to put on his increasing range of weapons.
The report in state media on Tuesday followed a series of missile launches — seven launch events in this month alone — and rising threats to use the weapons against his enemies.
North Korea's weapons tests and US-South Korea military exercises have intensified in a tit-for-tat cycle, underscoring heightened tensions in the region.
Officials say North Korea could further up the ante in the coming weeks or months with more provocative displays of its military nuclear program, possibly including its first test detonation of a nuclear device since September 2017.
The Korean Central News Agency said Mr Kim, during a meeting on Monday with officials and scientists at a state nuclear weapons institute, stressed the need to ramp up bomb fuel production to meet his goals to expand his nuclear arsenal "exponentially," and issued unspecified "important tasks" for his nuclear industry.
Mr Kim also examined the country's established plans for nuclear counterattacks as scientists briefed him on the North's latest nuclear-capable weapons systems and progress in technologies for mounting nuclear warheads on missiles, the agency said.
The agency's photos showed Mr Kim talking with officials inside a hall that displayed what appeared to be various types of warheads, including around 10 khaki-green capsules with red tips.
Other weapons included devices that looked like a black-and-white cone with fins or a large torpedo.
A wall poster near one of the green devices described a warhead called Hwasan-31, based on the Korean word for volcano.
The poster's graphics implied that the weapon could fit on some of North Korea's short-range ballistic systems, cruise missiles and a purported nuclear-capable underwater drone the country first unveiled last week.
State media didn't identify any of the devices in the photos.
The size and shape of the Hwasan-31, which some experts estimated was around 50 centimetres in width and 90cm in length, suggested progress in North Korean efforts to create a miniaturised warhead that could fit on various delivery systems, said Kim Dong-yub, a professor at the University of North Korean Studies in Seoul.
Lee Sung-jun, spokesperson of Seoul's Joint Chiefs of Staff, said the South's military was analysing the warhead unveiled in the North Korean photos but didn't offer specific assessments.
Mr Kim's calls for boosting bomb fuel production came days after Russian President Vladimir Putin announced plans to station tactical nuclear weapons in neighbouring Belarus, in what was seen as a warning to the West as it increases military support for Ukraine.
While aligning with Russia over its invasion of Ukraine, North Korea has stressed three-way cooperation with Moscow and Beijing to confront a "new Cold War" waged by "US imperialists," who it accuses of bringing the conflict to Asia by stepping up military activities with Seoul and Tokyo.
North Korea estimated to have 70kg of weapons-grade plutonium
Following six nuclear tests since 2006, North Korea likely has dozens of warheads that can probably be mounted on some of its older systems, like Scuds or Rodong missiles.
But there are differing assessments on how far North Korea has come in miniaturising and engineering those warheads so that they could fit on a variety of new weapons it developed at rapid pace in recent years, which may possibly require further technology upgrades or nuclear tests.
A biennial South Korean defence document released in February said North Korea is estimated to have 70 kilograms of weapons-grade plutonium, which some observers say is enough for about nine to 18 bombs.
The document estimated that North Korea has "a considerable amount of" highly enriched uranium as well.
North Korea's main nuclear complex in Yongbyon has facilities to produce both plutonium and highly enriched uranium, the two main bomb fuels used to build nuclear weapons.
North Korea is believed to be operating at least one additional covert uranium enrichment facility, in addition to the one at its Yongbyon complex.
Further missile tests as joint training continues
In separate reports, KCNA said the North again detonated mock warheads during tests of nuclear-capable missiles and a purported underwater attack drone this week.
The reports came a day after neighbouring militaries detected the North firing two short-range ballistic missiles toward waters off its eastern coast.
Monday's launches came hours before a nuclear-powered US aircraft carrier and its battle group engaged in joint training with South Korean warships in waters near Jeju island.
The USS Nimitz and the other warships pulled into the South Korean mainland port of Busan on Tuesday.
KCNA said the missiles tested on Monday were tipped with mock nuclear warheads that detonated as intended 500 metres above their sea targets.
A frontline unit fired the missiles as part of an exercise familiarising the troops with executing nuclear attack orders, the agency said.
North Korea earlier said some of its ballistic and cruise missile tests this month involved mock nuclear warheads detonated above their targets, communicating that it could control the height above ground to maximise an explosion's potential damage.
KCNA also said North Korea this week conducted another test of an alleged underwater nuclear attack drone capable of setting off a "radioactive tsunami" to destroy enemy naval vessels and ports.
North Korea had not indicated it was seeking such a capability before announcing last week that a previous test conducted on similar conditions was successful.
Analysts, however, are sceptical whether such a device would be a meaningful new threat, and South Korea's Joint Chiefs of Staff said on Monday it believes the North Korean claims regarding the weapon are likely "exaggerated or fabricated".
AP
