North Korea tested the capability of its missiles with multiple warheads, and in parallel sent dozens of balloons loaded with junk that landed in the South.
Relations between the two Koreas are at one of the lowest points in recent years, writes AFP.
Pyongyang is ramping up weapons testing as it bombards South Korea with balloons filled with junk, which it says are in retaliation for similar rockets sent by South Korean activists into the North.
Incheon Airport, Seoul's main hub, was forced to close on Wednesday because of the balloons, and in response to the back-to-back launches, South Korea completely suspended a military deal to reduce tensions and restarted propaganda broadcasts and firing exercises near the border.
North Korea claims it has "successfully conducted a control test of separation and guidance of individual mobile warheads," the state-run Korean Central News Agency announced on Thursday (June 27).
South Korea's military said Wednesday's North Korean test appeared to be the launch of a hypersonic missile, but the launch ended in a mid-air explosion.
Hong Min, a senior research fellow at the Korea Institute for National Unification, says multiple warhead missile technology is the ultimate goal for nations seeking missiles to carry nuclear warheads.
The North appears to be "testing such technology step by step over the long haul," he told AFP.
"It looks like they are making technological progress in the early stages of developing a multi-warhead missile."
The United States and Seoul often accuse North Korea of supplying Russia with ammunition and missiles for the war in Ukraine.
Russian President Vladimir Putin was in Pyongyang last week on a high-level state visit, when his growing ties with leader Kim Jong Un were highlighted.
The two signed a "breakthrough" agreement that included a promise that, in the event of an attack, the two countries would help each other.
South Korea, which announced last week that it would "reconsider" a long-standing policy barring direct arms supplies to Ukraine, announced on Thursday that it would impose unilateral sanctions against four Russian ships and eight North Korean individuals over arms shipments and oil transfers between the two countries.
Flash balloons
North Korea has sent hundreds of balloons carrying garbage to the South for three consecutive days in a "love for love" propaganda campaign.
Seoul's military said about 70 balloons had landed by Thursday morning, mostly in the northern Gyeonggi-do province and the Seoul area, and the contents were non-hazardous.
"The cargo is about ten kilograms, so there is a risk if the balloons descend quickly," the South Korean military said, adding that they were ready to respond.
South Korea's Marine Corps continued live-fire drills on islands near the western border between the two Koreas on Wednesday.
South Korea and the US held joint air exercises on Wednesday involving about 30 aircraft, including Washington's advanced stealth fighter F-22 Raptor.
South Korean President Jun Sukjul visited on Tuesday a US aircraft carrier that arrived in the country this week for joint military exercises aimed at countering threats from North Korea.
The exercises, which take place from Thursday to Saturday, include Washington's nuclear-powered aircraft carrier USS Theodore Roosevelt, Tokyo's guided-missile destroyer JS Atago and Seoul's KF-16 fighter jets, among others.
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