The move was most likely a routine test-firing but the official said it could also be meant to stoke tensions with Seoul.
The official said the projectiles flew about 120 miles before harmlessly landing in the water. They were fired from North Korea's eastern port city of Wonsan and the South Korean military is investigating the type of projectiles and the North's intentions.
Short-range test firings by North Korea are not unusual but a barrage of missile and artillery tests earlier this year boosted animosity between the rivals.
North Korea has in recent months threatened South Korea's leader.
The North's rising anger coincided with annual joint military exercises by the US and South Korea and a visit to Seoul by Barack Obama.