North Korea fired at least one ballistic missile off its east coast, South Korea and Japan confirmed Tuesday.
It is the latest in a series of weapons tests in recent weeks.
The ballistic missile was launched from Sinpo, Seoul's Joint Chief of Staff said.
"Our military is closely monitoring the situation and maintaining readiness posture in close cooperation with the United States, to prepare for possible additional launches," it added.
Japanese Prime Minister Fumio Kishida said two ballistic missiles were fired, calling the North's recent missile tests "very regrettable."
How significant is the latest missile test?
Sinpo, a major naval shipyard, is where the North keeps submarines, and equipment for testing submarine-launched ballistic missiles (SLBMs), according to satellite photographs.
The launch was the latest in a string of tests, which include a long-range cruise missile, a train-launched weapon, and what the North said was a hypersonic warhead.
A regional arms race is underway, with the South last month testing its first SLBM, becoming one of the few nations in the world to have demonstrated proven technology.
Intelligence chiefs to hold talks
The weapons test comes as Avril Haines, the US director of national intelligence, arrived in Seoul for a three-way meeting with her South Korean and Japanese counterparts on Tuesday.
The intelligence chiefs were scheduled to discuss the standoff with North Korea, amid other issues, according to reports.
The move also came after the US special representative on North Korea, Sung Kim, reiterated Washington's willingness for talks.
"We harbor no hostile intent toward (North Korea) and we are hopeful to meeting with them without conditions," he said following talks with his South Korean counterpart in Washington.