North Korea has fired around a dozen missiles off its eastern and western coasts, with at least one of them landing near the tense sea border with South Korea, after making veiled nuclear threats.
In response South Korea said its fighter jets fired three precision-guided missiles near the eastern border with the North.
It comes just hours after North Korea threatened to use nuclear weapons to get the US and South Korea to "pay the most horrible price in history" as it has intensified its fiery rhetoric targeting the ongoing large-scale military drills between its rivals.
South Korea's military said North Korea launched more than 10 missiles of various kinds off its eastern and western coasts. The Joint Chiefs of Staff had first said in a statement earlier on Wednesday that it detected three short-range ballistic missiles fired from the North's eastern coastal town of Wonsan.
It said one of the missiles landed in international waters, 16 miles south of the Koreas' eastern sea border and 104 miles northwest of South Korea's Ulleung island. It said it has issued the air raid alert on the Ulleung island.
The landing site is in international waters, but still far south of the extension of the nations' border. South Korea's military said it was the first time a North Korean missile had landed so close to the sea border since the countries' division in 1948.
"This is very unprecedented and we will never tolerate it," South Korea's Joint Chiefs of Staff said in a separate statement.
Animosities on the Korean Peninsula have been running high in recent months, with North Korea testing a string of nuclear-capable missiles and adopting a law authorising the pre-emptive use of its nuclear weapons in a broad range of situations.
Experts still doubt North Korea could use nuclear weapons first in the face of more superior US and South Korean forces.
North Korea has argued its recent weapons tests were meant to issue a warning to Washington and Seoul over their series of joint military drills that it views as an invasion rehearsal, including this week's exercises involving about 240 warplanes.
Pak Jong Chon, a secretary of the ruling Workers' Party who is considered a close confidant of leader Kim Jong-un, called the so-called "Vigilant Storm" air force drills "aggressive and provocative."
Mr Pak also accused the Pentagon of formulating a North Korean regime collapse as a major policy objective in an apparent reference to the Pentagon's recently released National Defence Strategy report. The report stated any nuclear attack by North Korea against the United States or its allies and partners "will result in the end of that regime".
He slammed South Korean military leaders over what he called "rubbish" comments that threatened to destroy North Korea if it uses nuclear weapons. South Korea's military has warned North Korea that using its nuclear weapons would put it on a "path of self-destruction".
"If the US and South Korea attempt to use armed forces against (North Korea) without any fear, the special means of the (North's) armed forces will carry out their strategic mission without delay," Mr Pak said, in an apparent reference to his country's nuclear weapons.
"The US and South Korea will have to face a terrible case and pay the most horrible price in history," he said.
US and South Korean officials have steadfastly said their drills are defensive in nature and that they have no intentions of attacking North Korea.
Mr Pak's statement is the North's second warning to the United States and South Korea this week. On Monday, the North's Foreign Ministry warned of "more powerful follow-up measures" in response to its rivals' air force drills.
South Korean officials have said North Korea could up the ante in coming weeks by detonating its first nuclear test device since September 2017, which could possibly take the country a step closer to its goals of building a full-fledged nuclear arsenal capable of threatening regional US allies and the American mainland.
Some experts say North Korea would eventually want to use its expanded nuclear arsenal as a leverage in future negotiations with the United States to win sanctions relief and other concessions.
