A TV screen shows a file image of North Korea's missile launch during a news program at Seoul Railway Station in Seoul, South Korea, Sept. 29. AP-Yonhap

North Korea fired two short-range ballistic missiles into the East Sea on Saturday, South Korea's military said, in its fourth such provocation in less than a week.

The Joint Chiefs of Staff (JCS) said it detected the launches from the Sunan area in Pyongyang between 6:45 a.m. and 7:03 a.m. and that the missiles flew some 350 kilometers at apogees of around 30 km at top speeds of Mach 6.

The launches came just hours before South Korea was set to hold an event marking the Armed Forces Day with its key military assets on display. The previous day, the South, the United States and Japan staged an anti-submarine warfare exercise in the East Sea.

"The recent series of North Korea's ballistic missiles is an act of significant provocation that undermines peace not only on the Korean Peninsula, but also in the international community, and a clear breach of U.N. Security Council resolutions," the JCS said in a text message sent to reporters.

It added, "Our military will maintain a firm readiness posture while tracking and monitoring related movements in close cooperation with the U.S. in preparation against additional provocations."

The presidential National Security Council convened a standing committee session and condemned the North's latest launches.