North Korea fired at least one ballistic missile off its east coast on Tuesday, officials in South Korea and Japan say.
South Korea's military confirmed that the missile was a submarine-launched ballistic missile.
The test comes as Seoul opens a major arms fair, spy chiefs meet to discuss the nuclear standoff and South Korea prepares for a space launch.
The North Korean launch is the latest weapons test by the country, which has pressed ahead with military development in the face of international sanctions imposed over its nuclear weapons and missile programmes.
One ballistic missile was launched about 10.17am local time near the port city of Sinpo, South Korea's Joint Chiefs of Staff (JCS) said, where North Korea keeps submarines as well as equipment for test firing submarine-launched ballistic missiles (SLBM).
North Korea has also launched other types of missiles from that area.
“Our military is closely monitoring the situation and maintaining readiness posture in close cooperation with the United States, to prepare for possible additional launches,” JCS said.
Japanese Prime Minister Fumio Kishida said two ballistic missiles had been detected and it was “regrettable” that North Korea had conducted a string of missile tests in recent weeks.
There was no immediate explanation from South Korea's JCS for the conflicting number of missiles detected.
