State media said North Korea's leader Kim Jong-un had urged his country to increase the production of "weapon-grade nuclear materials" and develop more potent weapons.
Kim's most recent threat, a reiteration of an earlier pledge to "exponentially" increase nuclear production, came the day before a US Navy carrier strike group arrived in South Korea.
According to the official Korean Central News Agency, Kim was briefed by officials from the country's nuclear weapons establishment and stated that North Korea should be prepared to utilize its nuclear weapons "at any time."
He urged officials to "increase the manufacturing of weapon-grade nuclear materials to achieve the plan for exponentially comprehensively expanding nuclear arsenals."
KCNA reported that Kim "incited the continued production of strong nuclear weapons."
According to the source, after North Korea has "flawlessly" prepared its nuclear weapons systems, "the adversary will fear us and not dare to challenge our state sovereignty, system, and people," Kim added.
'Irreversible' nuclear power
North Korea last year declared itself an "irreversible" nuclear power, and Kim recently called for an " exponential" increase in weapons production, including tactical nuclear weapons.
The nation is also attempting to diversify the delivery systems for its nuclear weapons; on Tuesday, it claimed to have performed a second successful test of its alleged underwater nuclear attack drone.
According to Pyongyang, the first test of the new weapon, Haeil, which means tsunami in Korean, was conducted last week in reaction to the most extensive US-South Korea military exercises in five years.
KCNA stated in a separate report that the new weapon simulated a 600-kilometre route for 41 hours and 27 minutes before exploding off the coast of North Hamgyong province early Monday morning.
The test "demonstrated all strategic qualifications as well as the system's safety and dependability," according to the KCNA report.
Russia is rumoured to have developed a similar weapon, the nuclear-capable Poseidon torpedo. Still, North Korea may not be able to master the complex technology required for such weapons, according to experts.
Separately, KCNA reported that the North Korean military conducted a firing exercise on Monday, simulating a nuclear attack using tactical ballistic missiles.