North Korea on Sunday launched a short-range missile into the Sea of Japan, the South Korean news agency Yonhap reported, citing the military.
The North had fired three short-range guided missiles into the sea on Saturday, dpa reported.
The reason for the launches remains unclear.
North Korea's missile and nuclear programmes are a source of international tension and sanctions, and the international community has been closely watching whether Pyongyang has developed the know-now to mount a nuclear warhead onto a missile.
The United States warned North Korea last month that the world would not allow it to become a nuclear power.