North Korea fired a ballistic missile towards the sea to the east of the Korean Peninsula on Saturday, the South Korean military said.
This is the first missile launch by North Korea in eight days and comes five days after Seoul accused Pyongyang of loosing five drones into South Korean airspace for the first time since 2017.
Japan's coastguard said North Korea had fired what could be a ballistic missile and sent notice about a possible second missile.
Pyongyang fired the missile a day after South Korea's defence ministry announced it had successfully conducted a test flight of a solid-propellant space launch vehicle.
On Monday, five North Korean drones crossed into South Korea, prompting South Korea's military to scramble fighter jets and attack helicopters to try to shoot them down.
One of them travelled as far as northern Seoul, causing security jitters among many people in South Korea and leading the military to offer a rare public apology on Tuesday.
Not counting Saturday, North Korea fired about 70 ballistic missiles about 38 times this year, Yonhap news agency said, including eight intercontinental ballistic missiles.
Some experts say North Korea is seeking to modernise its arsenal and increase its leverage in future dealings with the US.
The Saturday launch came as North Korea begins a major party meeting in Pyongyang to review past policies and new goals for 2023.
Some observers say North Korean leader Kim Jong-un will reaffirm his vow to expand his nuclear arsenal and introduce sophisticated weapons in the name of dealing with what he calls American hostility.
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News agencies contributed to this report