North Korea fired a suspected ballistic missile on Wednesday, Japan's defense ministry and South Korea's military said, hours after the United States separately deployed B-1B bombers for allied air drills.
No further information was immediately available.
The launch comes as South Korea and the United States prepare to wrap up 11 days of combined military drills, which Pyongyang has denounced.
The B-1B bombers conducted separate air drills with warplanes from South Korea and Japan earlier on Wednesday.
North Korea's ballistic missiles are banned by United Nations Security Council resolutions that have imposed strict sanctions on the nuclear-armed country.
(Reporting by Chang-Ran Kim in Tokyo and Josh Smith in Seoul; editing by Alison Williams and Alex Richardson)