Kim Min-seok, a ministry spokesman, said two missiles were launched in the morning in a northeasterly direction away from South Korean waters, while a third was launched in the afternoon.
A Seoul official, speaking on condition of anonymity, said based on the missiles' trajectory they did not appear to be medium- or long-range ballistic missiles.
"A more detailed analysis will be needed but the missiles launched may be a modified anti-ship missile or the KN-02 surface-to-surface missile derived from the Soviet era SS-21 that has a range of about 120 kilometers (74.5 miles)," the official said.
Kim Haing, a spokeswoman for the presidential office, said the South doesn't consider the missile launches a serious threat to security and that they appear to be tests.
"The situation is being monitored carefully," she said.
Pregnant Mila Kunis wins 'Best Villain' at MTV Movie Awards
Biologists detail four new deep-sea 'killer sponges'