Pyongyang says any territorial violations during annual US-South Korea military exercises will be met with force.
North Korea fired what appeared to be multiple land-to-ship missiles off its east coast on Thursday, South Korea’s military said.
The projectiles were launched Thursday morning from the North Korean coastal city of Wonsan, South Korea’s Office of Joint Chiefs of Staff said in a statement.
The missiles flew about 200km, it said.
Isolated but nuclear-armed, North Korea has test-fired a missile almost every week for the past few weeks.
“North Korea fired multiple unidentified projectiles, assumed to be surface-to-ship missiles, this morning from the vicinity of Wonsan, Gangwon province,” the South’s military said.
The Japanese government also confirmed the missile launches, according to the Kyodo news agency.
“We have not confirmed any immediate effect to our nation’s security, at this point. We will continue to coordinate with the United States and South Korea to gather and analyse information, and maintain a high level of alert,” said Japanese Foreign Minister Fumio Kishida.
The statement by South Korea said the launches were immediately reported to President Moon Jae-in but gave no further details
The missile tests – and Pyongyang’s threat to stage its sixth nuclear test – have prompted calls for tougher United Nations sanctions and a warning from US President Donald Trump that military intervention was an option under consideration.
The launches come less than a week after the UN Security Council passed new sanctions on the reclusive state, which said it would continue to pursue its nuclear and weapons programme without delay.
Pyongyang has slammed the latest UN sanctions as “mean”.
North Korea has conducted dozens of missile tests since the start of last year, as well as its fourth and fifth nuclear bomb tests.
It has said it is working to develop a nuclear-tipped intercontinental ballistic missile (ICBM) capable of reaching mainland United States, presenting Trump with perhaps his most pressing security threat.
The head of the US Missile Defense Agency, Vice Admiral James Syring, said on Wednesday that the technological advances demonstrated by North Korea in its ballistic missile programme over the past six months had caused him “great concern”.
Syring told a hearing of the US House Armed Services Committee that it was incumbent on his agency to assume that North Korea today could “range” the US with an ICBM carrying a nuclear warhead.
“I would not say we are comfortably ahead of the threat; I would say we are addressing the threat that we know today,” Syring said.
“The advancements in the last six months have caused great concern to me and others, in the advancement of and demonstration of technology of ballistic missiles from North Korea. It is incumbent on us to assume that North Korea today can range the United States with an ICBM carrying a nuclear warhead.”
North Korea’s weapons tests are meant to build a nuclear and missile programme that can stand up to what it sees as US and South Korean hostility, but they are also considered by analysts as ways to make its political demands clear to leaders in Washington and Seoul.
These demands include the removal of nearly 30,000 US troops in South Korea meant to check North Korean aggression.
Professor Yang Moo-jin, of the University of North Korean Studies in Seoul, told AFP news agency: “North Korea has been stepping up missile tests … in order to project an image to the world that international sanctions can never bring it to its knees.
“It is also expressing displeasure of the arrival of a US nuclear submarine in South Korean”.
The 6,900-tonne USS Cheyenne, whose home port is Pearl Harbor, arrived in the South Korea port of Busan on Tuesday.