Japanese Prime Minister Shinzo Abe said he was convening an emergency meeting of officials after the launch.
Japanese public broadcaster NHK said the North Koreans fired a projectile shortly before midnight Japan time (5 p.m. Prague time) on July 28.
It said the projectile may have landed in Japan's exclusive economic zone.
Even before the latest launch, tensions were high on the Korean Peninsula, with the United States, Japan, and South Korea repeatedly expressing condemnation of previous test launches by Pyongyang.
North Korea’s nuclear and ballistic-missile programs are banned by United Nations resolutions, but Pyongyang has continued the tests, saying they are necessary to prevent aggression by the United States.
On July 27, U.S. General Mark Miller, the Army chief of staff, warned that North Korea’s ability to launch a missile capable of reaching the United States was advancing significantly and faster than expected.
Miller said "time is running out” for a diplomatic solution to the crisis over Pyongyang’s weapons program.
The U.S. Senate on July 27 nearly unanimously approved tough sanctions on Russia, Iran, and North Korea and has sent the legislation to the White House pending President Donald Trump's signature.
On July 4, North Korea conducted its first-ever successful launch of an intercontinental ballistic missile (ICBM) that Washington said can likely carry a nuclear warhead and threaten the United States.
That launch came after Trump assailed North Korea’s “reckless and brutal regime” and said there was a “strong, solid plan” to deal with Pyongyang’s illicit nuclear and ballistic-missile programs.
The U.S. Missile Defense Agency said on July 11 that it conducted a successful test from Kodiak, Alaska, of the Terminal High Altitude Area Defense, part of the United States' ballistic-missile defense system.
The agency said a THAAD weapon system detected, tracked, and intercepted a test target, which was similar to missiles recently tested by North Korea.