North Korea has fired more missiles in the last 24 hours than it did during the whole of 2017 -- the year of "fire and fury" when leader Kim Jong Un traded barbs with then-US president Donald Trump.
What has triggered the record-breaking blitz of weapons tests? Analysts say ongoing US-South Korean military exercises are a key factor, and warn that Kim is building up to another nuclear test.
AFP takes a look at what's going on:
Seoul and Washington are carrying out their largest ever joint air drills, called Vigilant Storm, which involve hundreds of warplanes from both sides staging mock attacks 24 hours a day.
The drills, originally due to end Friday, will be extended, South Korea's air force said, to "maintain ironclad security joint posture" in the face of North Korean aggression.
The complex annual exercises take "months of planning and preparation", South Korea's air force says.
This year, about 240 American and South Korean warplanes will conduct around 1,600 sorties, which is "the largest number ever" for these drills, it added.
The exercises "strengthen the operational and tactical capabilities of combined air operations", it said.
The drills involve some of South Korea and America's advanced fighter jets -- F-35As and F-35Bs, both of which are stealth aircraft designed to produce as small a radar signature as possible.
North Korea may have nuclear weapons -- which the South does not -- but its air force is the weakest link in its military, analysts say, and is likely unable to counter stealth aircraft technology.
"Most of North Korea's aircraft are outdated... they have very few state-of-the-art fighter jets," Cheong Seong-chang, researcher at the Sejong Institute, told AFP.
"The North does not have much oil needed for aircraft, so training is also not being done properly," he added.
The stealth jets, experts say.
This summer there were reports that US and South Korean commandos were practising so-called "decapitation strikes" -- the removal of North Korea's top leadership in a lightning-fast military operation.
Pyongyang's blitz of launches this week are "because of Vigilant Storm which includes the F-35 stealth fighter jets", said Go Myong-hyun, a researcher at the Asan Institute for Policy Studies.
Pyongyang believes stealth jets would "be used in decapitation operations", Go added.
Experts say there are additional signs that Kim is concerned, pointing to a revision of North Korea's nuclear law this September.
The new law, which allows for a first nuclear strike, placed Pyongyang's nukes under Kim's "monolithic command".
If North Korea's nuclear "command and control system" -- Kim -- is "placed in danger owing to an attack by hostile forces, a nuclear strike shall be launched automatically and immediately", it says.
Pyongyang calls Vigilant Storm "an aggressive and provocative military drill targeting the DPRK".
Even the name offends the North, which claims it harks back to Operation Desert Storm, the US-led military assault on Iraq in 1990-1991 after the invasion of Kuwait.
The US and South Korean militaries have been training together for years, and the joint drills have long infuriated Pyongyang, which sees them as rehearsals for war.
It has repeatedly justified its missile launches as necessary "countermeasures" to what it calls America's "hostile" policies.
Its supporters in Beijing and Moscow agree, and have blocked US-led attempts to sanction Pyongyang at the United Nations over its tests, saying Washington is responsible for provoking the North with the drills.
"But the Kim regime threatens regional peace with illegal weapons primarily because of its revisionist goals against South Korea, not because of a particular action Washington does or does not take," said Leif-Eric Easley, a professor at Ewha University in Seoul.
South Korea's hawkish President Yoon Suk-yeol took office in May vowing to get tough with Pyongyang.
He has dramatically ramped up joint drills, which had been scaled back during the pandemic or paused for a bout of ill-fated diplomacy.
Since talks collapsed in 2019, North Korea's Kim has doubled down on his banned weapons programmes, conducting repeated tests of bigger and ever more threatening weapons.
Washington and Seoul have been warning for months that the recent missile launches could culminate in another nuclear test -- which would be Pyongyang's seventh.
The United States stations around 27,000 troops in South Korea to help defend it against the North, and the allies say joint drills are an essential part of their defence strategy.
