North Korea has fired a missile over Japan and into waters off the northern region of Hokkaido, marking a sharp escalation of tensions on the Korean peninsula.
The test, which experts said appeared to have been an intermediate-range Hwasong 12 missile, came as US and South Korean forces conduct annual military drills on the peninsula, against which North Korea strenuously objects.
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North Korea has conducted dozens of ballistic missile tests under young leader Kim Jong-Un, the most recent on Saturday, but firing projectiles over mainland Japan is rare.
"North Korea's reckless action is an unprecedented, serious and grave threat to our nation," Japanese Prime Minister Shinzo Abe told reporters.
Abe said Japan was seeking an urgent meeting at the United Nations to strengthen measures against Pyongyang.
The test was a clear violation of UN resolutions and the government had protested against the move in the strongest terms, he said.
Japan's Chief Cabinet Secretary Yoshihide Suga said the latest North Korean missile fell into the sea 1180km east of the Cape of Erimo on Hokkaido.
"It is an unprecedented, serious and grave threat to our nation," Suga told a briefing, adding the government had protested the move in the strongest terms.
The Japanese government's J-Alert system broke into radio and TV programming, warning citizens of the possible missile.
Bullet train services were temporarily halted and warnings went out over loudspeakers in towns in Hokkaido.
South Korea's military said the missile was launched from the Sunan region near the North Korean capital just before 6am (am NZT). It flew 2700 km, reaching an altitude of about 550km.
Japanese public broadcaster NHK reported the missile broke into three pieces and fell into waters off Hokkaido.
The Japanese military did not attempt to shoot down the missile, which passed over Japanese territory at 6:07am (local time).
Earlier this month, North Korea threatened to fire missiles into the sea near the US Pacific territory of Guam, after US President Donald Trump warned
Pyongyang would face "fire and fury" if it threatened the United States.
In Washington, the Pentagon confirmed the missile flew over Japan but did not pose a threat to North America and said it was gathering further information.
North Korea has again asked the UN Security Council to meet to discuss the ongoing joint US-South Korean military drills, according to a letter released on Monday by the North Korean mission to the United Nations.
The August 25 letter to the Security Council and Secretary-General Antonio Guterres, from North Korean UN Ambassador Ja Song Nam, described the military exercises as a "grave threat" to the Korean peninsula and international peace and security.
"It is the fair and square self-defensive right of the DPRK to cope with reckless, aggressive war manoeuvres and the US would be wholly responsible for any catastrophic consequences to be entailed from the result," Ja wrote, using the initials of North Korea's official name, the Democratic People's Republic of Korea.
Previous requests have gone unanswered by the 15-member Security Council.
The 15-member UN Security Council unanimously imposed new sanctions on North Korea in response to the two July long-range missile launches.