The South's Joint Chiefs of Staff said the missile was fired on Monday from an area near the North Korean capital of Pyongyang but did not immediately release more specific flight details.
The joint chiefs said the military was strengthening its surveillance and defence posture in preparation for possible additional launches and sharing information on the missile with the United States and Japan.
Japan's defence ministry said the missile landed outside its exclusive economic zone and there were no reports of damage to vessels or aircraft.
The launch came as US Secretary of State Antony Blinken was visiting Seoul for talks with South Korean allies over the North Korean nuclear threat and other issues.
US Secretary of State Antony Blinken has met South Korean counterpart Cho Tae-yul in Seoul. (AP PHOTO)
Blinken's visit comes amid political turmoil in South Korea following President Yoon Suk-yeol's short-lived martial law decree and subsequent impeachment by parliament in December, which experts say puts the country at a disadvantage in getting a steady footing with Trump before his return to the White House.
In a news conference with South Korean Foreign Minister Cho Tae-yul, Blinken said they condemned North Korea's latest launch, which violates UN Security Council resolutions against the North, and reiterated concerns about the growing alignment between Pyongyang and Moscow over Russian President Vladimir Putin's war on Ukraine.
According to US, Ukrainian and South Korean assessments, North Korea has sent more than 10,000 troops and conventional weapons systems to support Moscow's war against Ukraine.
There are concerns that Russia could transfer North Korea advanced weapons technology in return, which could potentially enhance the threat posed by leader Kim Jong-un's nuclear-armed military.
Blinken and Cho dismissed concerns about damage to the US-South Korea alliance in the aftermath of the political turmoil in Seoul.
Experts had warned that Yoon's martial law decree - which lasted only hours but has rattled politics, high-level diplomacy and financial markets for weeks - exposed the fragility of South Korea's democratic system in a divided society.
In a year-end political conference, North Korean leader Kim vowed to implement the "toughest" anti-US policy and criticised the Biden administration's efforts to strengthen security cooperation with Seoul and Tokyo, which he described as a "nuclear military bloc for aggression".
North Korean state media did not specify Kim's policy plans or mention any specific comments about Trump.
During his first term, Trump met Kim three times for talks on the North's nuclear program.
Many experts, however, say a quick resumption of Kim-Trump summitry is unlikely because Trump would first focus on conflicts in Ukraine and the Middle East.
Before his presidency faltered over the ill-conceived power grab, Yoon worked closely with US President Joe Biden to expand joint military exercises, update nuclear deterrence strategies and strengthen trilateral security cooperation with Tokyo.
