North Korea fired a ballistic missile over the sea to the east of the Korean Peninsula in the early hours of Sunday, Yonhap news agency reported citing the South Korean military.
The move comes not even 24 hours after North Korea launched three ballistic missiles on Saturday.
The short-range ballistic missile was fired around 2:50 a.m. local time (0750 GMT) from Pyongyang, Yonhap said, citing South Korea's Joint Chiefs of Staff.
The launch follows an unprecedented number of missile tests conducted by North Korea this year, as Pyongyang presses on with weapons development amid speculation it could test a nuclear weapon for a seventh time.