A brief statement from South Korea's Joint Chiefs of Staff gave no further details such as how far the weapon flew.
The launch comes days before South Korea hosts the Asia-Pacific Economic Conference. U.S. President Donald Trump, Chinese President Xi Jinping and other world leaders are to gather in the South Korean city of Gyeongju for talks next week.
Earlier this month, North Korean leader Kim Jong Un displayed a new long-range missile at a massive military parade in Pyongyang, with top Chinese, Russian and other leaders present. The parade, which marked the 80th anniversary of the founding of the ruling Workers' Party, highlighted Kim's growing diplomatic footing and his relentless drive to build an arsenal that could target the continental United States and his rivals in Asia.
Kim's diplomatic credentials have been bolstered recently. He took center stage with Chinese leader Xi Jinping and Russian President Vladimir Putin at a Beijing military parade last month. U.S. President Donald Trump and South Korean President Lee Jae Myung have also repeatedly expressed hopes to meet Kim as he flaunts a provocative nuclear program.