North Korea fired several rounds of short-range ballistic missiles toward the East Sea on Monday, the South Korean military said, three days after it launched cruise missiles into the Yellow Sea. The Joint Chiefs of Staff (JCS) said it detected what appeared to be several short-range ballistic missiles launched from the Pyongyang region at 3:01 p.m. "The North Korean missiles flew about 300 kilometers and splashed into the sea," the JCS said in a text message to reporters. It did not provide further details, citing an ongoing analysis. The JCS denounced the North's missile launches as "a clear provocation" that seriously threatens peace and stability on the Korean Peninsula, vowing to maintain heightened vigilance against its additional launches. It marks the North's first ballistic missile launch since it test-fired a new intermediate-range ballistic missile tipped with a hypersonic warhead. North Korea said it conducted a "super-large warhead" power test for a strategic cruise missile and test-fired a new anti-aircraft missile in the Yellow Sea on Friday. North Korea has been ramping up weapons tests this year, including the launches of cruise missiles and ballistic missiles with a hypersonic controllable warhead and firing drills involving super-large multiple rocket launchers. A hypersonic missile is usually hard to intercept with existing missile defense shields. It travels at a speed of at least Mach 5 -- five times the speed of sound -- and is designed to be maneuverable on unpredictable flight paths and fly at low altitudes. The South Korean military is closely monitoring as North Korea was believed to be preparing to place a second spy satellite into space after its first launch in November. Source: Yonhap News Agency