North Korea test-fired what appeared to be a hypersonic missile on Wednesday, but the launch ended in a mid-air explosion, an official from Seoul's Joint Chiefs of Staff said.
The early morning launch came just hours after Pyongyang sent another flurry of trash-bearing balloons southward, this time forcing a three-hour halt to flights in and out of South Korea's Incheon airport.
The missile took off from an area in or around Pyongyang at about 5:30 am (2030 GMT) and South Korean and US intelligence agencies were conducting a detailed analysis, Seoul's Joint Chiefs of Staff said in a statement.
The JCS official said the test of what appeared to be a hypersonic missile ended in failure after a journey of some 250 kilometers.
More smoke than usual appeared to emanate from the missile, raising the possibility of combustion issues, the official said, adding it may have been powered by solid propellants.
Japan also confirmed the launch, with its coast guard saying the missile splashed down in the Sea of Japan, also known as the East Sea.
"Vessels please be careful about information to come and refrain from approaching if fallen objects are spotted, and report relevant information to the coast guard," it said on its website.
The test follows North Korea launching hundreds more trash-carrying balloons southward on Monday and Tuesday, the latest in a series of border barrages that have sparked a tit-for-tat propaganda campaign.
Seoul's military said the balloons were carrying "mostly paper waste" that posed no safety risk to the public.
But the latest batch of North Korean balloons disrupted takeoffs and landings at Incheon International Airport, an official told AFP.
Both domestic and international flight arrivals and departures "were suspended ... from 1:46 am (1646 GMT) to 4:43 am," an Incheon International Airport Corporation official said.
"At around 4:08 am, it was confirmed that a trash-carrying balloon had fallen near Gate 248 of T2, and military authorities collected it. The airport is operating as normal since 4:44 a.m," the official added.
Pyongyang has already sent more than a thousand balloons carrying trash in what it says is retaliation for balloons carrying propaganda criticising Kim's rule floated north by activists.
In response, Seoul has fully suspended a tension-reducing military deal and restarted some propaganda broadcasts from loudspeakers along the border.
Kim Jong Un's sister and key government spokeswoman Kim Yo Jong warned this month that Seoul would "undoubtedly witness the new counteraction of the DPRK" if the leaflet drops and loudspeaker broadcasts continued.
An activist in the South confirmed Friday that he had launched more balloons.
Legally, South Korea cannot sanction activists sending balloons across the border due to a 2023 court ruling that bans it as an unjustifiable infringement on free speech.
Experts have warned that the balloons inadvertently cause border tensions to escalate quickly.
On Tuesday, Yoon visited a US aircraft carrier that arrived in South Korea at the weekend for joint military drills aimed at countering North Korean threats.
The drills, which include Japan, are set to go ahead later this month.
Pyongyang has routinely criticised such exercises as rehearsals for an invasion.
North Korea's last missile launch before Wednesday's failed test came on May 30, when Seoul accused Pyongyang of firing a volley of around 10 short-range ballistic missiles.
Analysts have suggested the nuclear-armed North could be testing and ramping up production of artillery and cruise missiles before sending them to Russia for use in Ukraine.
