SEOUL, SOUTH KOREA -- 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.
North Korean photos of the meeting also showed what appeared to be a small new tactical warhead that was possibly designed to fit on a variety of delivery systems developed in recent years to overwhelm South Korean defences.
The report in state media 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 U.S.-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 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 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.
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 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 (19 inches) wide and 90 centimetres (35 inches) long, suggested progress in North Korean efforts to create a miniaturized warhead that could fit on its delivery systems, said Kim Dong-yub, a professor at the University of North Korean Studies in Seoul.
Cheong Seong-Chang, an analyst at South Korea's Sejong Institute, said the reports suggest North Korea is moving closer to its next nuclear test.
Hours before North Korea's sixth test in 2017, state media showed Kim Jong Un observing a silver, peanut-shaped device, which apparently was a purported thermonuclear weapon built for intercontinental ballistic missiles the North claimed to have detonated during that test.
Cheong said the North will likely use its next test to claim it acquired a miniaturized nuclear warhead to mount on a growing range of weapons it describes as "tactical." The North's use of the term communicates a threat to proactively use them during conflicts to blunt the stronger conventional forces of South Korea and the United States.
North Korea likely has dozens of nuclear warheads that can probably be fitted on some of its older systems, like Scuds or Rodong missiles.
Lee Sung-jun, spokesperson of Seoul's Joint Chiefs of Staff, said the South's military was analyzing the warhead unveiled in the North Korean photos but didn't provide specific assessments.
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 "U.S. imperialists," who it accuses of bringing the conflict to Asia by stepping up military activities with Seoul and Tokyo.
A biennial South Korean defence document released in February said North Korea is estimated to have 70 kilograms (154 pounds) 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 Yongbyon..
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 neighboring militaries detected the North firing two short-range ballistic missiles off its eastern coast.
Monday's launches came hours before a nuclear-powered U.S. aircraft carrier and its battle group engaged in joint training with South Korean warships in waters near Jeju island, in the allies' latest show of strength. The USS Nimitz and the other warships pulled into the South Korean mainland port of Busan on Tuesday.
The North's official Rodong Sinmun newspaper on Tuesday published a commentary condemning the allies' exercises and the U.S. deployment of the Nimitz strike group in the Korean Peninsula, insisting that the move "amounts to an open declaration of war."
KCNA said the missiles tested Monday were tipped with mock nuclear warheads that detonated as intended 500 metres (1,640 feet) above their sea targets. A front-line unit fired the missiles as part of an exercise familiarizing the troops with executing nuclear attack orders, the agency said.
KCNA also said North Korea this week conducted another test of an underwater nuclear attack drone capable of setting off a "radioactive tsunami" to destroy enemy vessels and ports. Analysts, however, are skeptical whether such a device was a new threat, and South Korea's Joint Chiefs of Staff said Monday it believes the North Korean claims regarding the weapon are likely "exaggerated or fabricated."
Still, the drone underlines Kim's commitment to spur the expansion of his nuclear arsenal as he seeks to force the United States to accept the North as a legitimate nuclear power and negotiate economic concessions from a position of strength.
North Korea already is coming off a record year in weapons testing, launching more than 70 missiles in 2022. It had set into law an escalatory nuclear doctrine that authorizes pre-emptive nuclear strikes in a broad range of scenarios where it may perceive its leadership as under threat.
