North Korea claims a fifth ballistic missile launch this month served as a simulated nuclear attack on South Korea.
Pyongyang has responded angrily to the largest joint military exercises in years between the United States and South Korea.
Kim Jong-un ordered a series of military drills and missile launches as push back against the “aggression” being displayed by his enemies, according to state media.
South Korea and Japan's militaries detected the short-range missile being launched on Sunday into waters off the North's eastern coast, which reportedly came less than an hour before the US flew long-range B-1B bombers for training with South Korean warplanes.
The North characterises the US-South Korea exercises as a rehearsal to invade, though the allies insist they are defensive in nature.
Some experts say the North uses the exercises as a pretext to advance its weapons programmes.
Pyongyang's official Korean Central News Agency said the missile, which flew about 800 kms, was tipped with a mock nuclear warhead.
It described the test as successful, saying that the device detonated as intended 800m above water at a spot that simulated an unspecified "major enemy target," supposedly reaffirming the reliability of the weapon's nuclear explosion control devices and warhead detonators.
The report said the launch was the final step of a two-day drill that also involved nuclear command and control exercises and training military units to switch more quickly into nuclear counter-attack posture, properly handle nuclear weapons systems and execute attack plans.
The exercise was also a "stronger warning" to the United States and South Korea, who are "undisguised in their explicit attempt to unleash a war" against the North, KCNA said.
Photos published by state media showed Kim walking through a forest with his daughter and senior military officials and a missile the North described as a tactical nuclear weapon system soaring from the woods spewing flames and smoke.
Saying that his enemies are getting "ever more pronounced in their moves for aggression," Kim laid out unspecified "strategic tasks" for further developing his nuclear forces and improving their war readiness, KCNA said.
This indicated that the North could up the ante in its weapons demonstrations in coming weeks or months.
Jeon Ha Gyu, spokesperson of South Korea's defence ministry, said it's clear North Korea with its ramped-up testing activity is making "considerable progress" in nuclear weapons technology.
He did not provide a specific assessment about the North's claim about the successful warhead detonation.
Sunday's short-range launch was the North's fifth missile event this month and the third since the US and South Korean militaries began joint exercises on March 13.
The allies' drills, which are to continue through Thursday, include computer simulations and their biggest springtime field exercise since 2018.
The North so far in 2023 has fired around 20 missiles over nine different launch events. They included short-range missiles fired from land, cruise missiles launched from a submarine, and two different intercontinental ballistic missiles fired an airport near Pyongyang.
