The South Korean military called it a "highly unusual" move designed to show the allies' resolve to respond to any threats from North Korea.
The fire was caused by burning rocket propellant, and although the missile carried a warhead, it did not explode, South Korea's military said.It's not rare for military hardware to fail, and North Korea has suffered several failed missile launches this year as well.It was the first North Korean missile to follow a trajectory over Japan since 2017, and its estimated 4,600 km (2,850 mile) flight was the longest for a North Korean test, which are usually "lofted" into space to avoid flying over neighbouring countries.Analysts and security officials said it may have been a variant of the Hwasong-12 IRBM, which North Korea unveiled in 2017 as part of what it said was a plan to strike U.S.The flight has increased concerns that North Korea may soon conduct an expected nuclear test, which would be the first since 2017.South Korean officials said North Korea had completed preparations for a test and might use a smaller weapon meant for operational use, or a big device with a higher yield than in previous tests.