The latest test comes as both Koreas are building up their weapons capabilities in what could become an arms race on the peninsula.
North Korea has fired a suspected submarine-launched ballistic missile into the sea.
The "short-range ballistic missile suspected to be an SLBM (submarine-launched ballistic missile)" was fired from Sinpo into the sea east of the peninsula, South Korea's Joint Chiefs of Staff said in a statement on Tuesday.
Japanese Defense Minister Nobuo Kishi said, however, his country’s initial analysis suggested that the North fired two ballistic missiles.
Japan’s coast guard issued a maritime safety advisory to ships but didn’t immediately know where the missiles landed.
DPRK's focus on submarine production
The shipyard in Sinpo is a major defence industry hub where North Korea focuses its submarine production and the country has also used those facilities in recent years to develop ballistic weapons systems designed to be fired from submarines.
A test of a submarine-launched ballistic missile, which would be North Korea’s first since 2019, would be the country’s most significant military demonstration since the US President Joe Biden took office and underscore how it continues to expand its nuclear weapons capabilities amid a pause in diplomacy.
South Korean officials held a national security council meeting and expressed “deep regret” over the launch that came amid efforts to revive diplomacy.
Nuclear negotiations between Washington and Pyongyang have stalled for more than two years over disagreements in exchanging the release of crippling US-led sanctions against North Korea and the North’s denuclearisation steps.