North Korea appeared to have fired two cruise missiles Tuesday morning, South Korea's military said, in what would be the nuclear-armed country's fifth weapons test this month.
Pyongyang has rebuffed US offers of talks and embarked on a flurry of sanctions-busting tests in 2022, flexing its military muscles and ramping up the rhetoric against Washington.
The US and South Korean intelligence agencies are analysing the launch, the JCS added.
Since leader Kim Jong Un avowed his commitment to military modernisation at a key party speech in December, North Korea has conducted a string of weapons tests.
Washington imposed fresh sanctions earlier this month, which Pyongyang called a "provocation", later hinting it could resume banned nuclear and long-range weapons tests in response.
North Korea's cruise missile launches are not banned under the current United Nations sanctions regime.
The tests come at a delicate time in the region, with Kim's sole major ally China set to host the Winter Olympics next month and South Korea gearing up for a presidential election in March.
Russia and China last week blocked the UN Security Council from imposing fresh sanctions in response to the recent tests.