North Korea fired what could be a ballistic missile on Saturday, Japan's military and South Korean media said.
South Korea's military said North Korea fired a projectile off its east coast, and Yonhap news agency said the military believed it was a ballistic missile.
Japan's defence ministry also tweeted that the projectile could be a ballistic missile.
On Wednesday, North Korea fired a ballistic missile toward the sea off its east coast, South Korea and Japan said, after Pyongyang vowed to develop its nuclear forces "at the fastest possible speed".
The United States assessed that North Korea was preparing its Punggye-ri nuclear test site and could be ready to conduct a test there as early as this month, State Department deputy spokesperson Jalina Porter said.
South Korea's president-elect Yoon Suk-yeol takes office on Tuesday.