North Korea launched a ballistic missile early Tuesday (local time) toward the East Sea, South Korea's military said, referring to the body of water also known as the Sea of Japan.
The Japanese government also said North Korea fired what could be a ballistic missile.
The latest launch comes just days after Pyongyang announced it tested an intercontinental ballistic missile, prompting condemnation from the South, the United States and Japan.
North Korea has upped its rhetoric in recent months and has also staged dozens of launches of missiles this year, most recently in mid-September, when it fired a salvo of short-range ballistic missiles.
In July, the country tested a new tactical ballistic missile capable of carrying a 4.5-ton super-large warhead.
Two weeks ago, North Korean leader Kim Jong Un inspected key missile bases, reviewing the "readiness for action of strategic deterrence" and describing US strategic nuclear capabilities as a threat.
Kim stressed the need to prioritize the strategic missile force in the modernization of the country's armed forces, calling it "an important principle of the strategy for building the national defense."