The message in the country's state media quoted Kim and was directed at "South Korean military warmongers." It comes as U.S. and North Korean officials struggle to set up talks after a recent meeting on the Korean border between Kim and President Donald Trump seemed to provide a step forward in stalled nuclear negotiations.
Although the North had harsh words for South Korea, the statement stayed away from the kind of belligerent attacks on the United States that have marked past announcements, a possible signal that it's interested in keeping diplomacy alive.
It made clear, however, that North Korea is infuriated over Seoul's purchase of U.S.-made high-tech fighter jets and U.S.-South Korean plans to hold military drills this summer that the North says are rehearsals for an invasion and proof of the allies' hostility to Pyongyang.
After watching the weapons' launches, Kim said they are "hard to intercept" because of the "low-altitude gliding and leaping flight orbit of the tactical guided missile," according to the Korean Central News Agency. He was quoted as saying the possession of "such a state-of-the-art weaponry system" is of "huge eventful significance" in bolstering his country's armed forces and guaranteeing national security.
South Korean officials said Thursday the weapons North Korea fired were a new type of a short-range ballistic missile and that a detailed analysis is necessary to find out more about the missiles. But many civilian experts say the weapons are likely a North Korean version of the Russian-made Iskander, a short-range, nuclear-capable ballistic missile that has been in the Russian arsenal for more than a decade.
That missile is designed to fly at a flattened-out altitude of around 40 kilometers (25 miles) and make in-flight guidance adjustments. Both capabilities exploit weaknesses in the U.S. and South Korean missile defenses that are now in place, primarily Patriot missile batteries and the THAAD anti-missile defense system. The Iskander is also quicker to launch and harder to destroy on the ground, because of its solid fuel engine. It advanced guidance system also makes it more accurate.
The launches were the first known weapons tests by North Korea in more than two months. When North Korea fired three missiles into the sea in early May, many outside experts also said at the time those weapons strongly resembled the Iskander.
The North Korean message Friday was gloating at times, saying the test "must have given uneasiness and agony to some targeted forces enough as it intended."
KCNA accused South Korea of "running high fever in their moves to introduce the ultramodern offensive weapons."
North Korea likely referred to South Korea's purchase and ongoing deployment of U.S.-made F-35 fighter jets. Earlier this month, North Korea said it would develop and test "special weapons" to destroy the aircraft. Under its biggest weapons purchase, South Korea is to buy 40 F-35 fighter jets from Lockheed Martin by 2021. The first two arrived in March and two others are to be delivered in coming weeks.
South Korea's Unification Ministry on Friday described the launches as "acts of provocation" that are "not helpful to an efforts to alleviate military tensions on the Korean Peninsula."
In Washington, State Department spokeswoman Morgan Ortagus urged "no more provocations," saying the U.S. is committed to diplomatic engagement with North Korea. "We continue to press and hope for these working-level negotiations to move forward," she said.
North Korea is banned by U.N. Security Council resolutions from engaging in any launch using ballistic technology. While the North could face international condemnation over the latest launches, it's unlikely that the nation, already under 11 rounds of U.N. sanctions, will be hit with fresh punitive measures. The U.N. council has typically imposed new sanctions only when the North conducted long-range ballistic launches.
North Korea has been urging the U.S. and South Korea to scrap their military drills. Last week, it said it may lift its 20-month suspension of nuclear and long-range missile tests in response. Seoul said Wednesday that North Korea was protesting the drills by refusing to accept its offer to send 50,000 tons of rice through an international agency.
North Korea also may be trying to get an upper hand ahead of a possible resumption of nuclear talks. Pyongyang wants widespread sanctions relief so it can revive its dilapidated economy. U.S. officials demand North Korea first take significant steps toward disarmament before they will relinquish the leverage provided by the sanctions.
U.N. Secretary-General Antonio Guterres called for the swift resumption of talks between the United States and North Korea following the new missile launches.
China, the North's last major ally and biggest aid provider, said both Washington and Pyongyang should restart their nuclear diplomacy as soon as possible.
"North Korea appears to be thinking its diplomacy with the U.S. isn't proceeding in a way that they want. So they've fired missiles to get the table to turn in their favor," said analyst Kim Dae-young at the Korea Research Institute for National Strategy.