"It is one of the routine missile tests North Korea carries out every year," the source said.
"We consider today's launch as part of routine military training as was the May 25 launch."
In May, North Korea launched missiles into the Sea of Japan (East Sea), the first such test in nearly a year.
The tests come as the US and other negotiators try to settle a banking dispute which has so far blocked a start to North Korea's promised nuclear disarmament.
In July last year it test-fired seven missiles, including Taepodong-2 missiles that theoretically can reach the US west coast.
The July launch brought UN condemnation and missile-related sanctions.
Raising further alarm in the international community, in October last year North Korea carried out its first nuclear armaments test.
Analysts believe Pyongyang does not yet possess the expertise to miniaturise a nuclear warhead to fit on a missile.