South Korea's military has asserted that parts of North Korea's claim to have fired strategic cruise missiles are exaggerated and not factual.

In a notice to the local press on Monday, the Joint Chiefs of Staff(JCS) said Seoul and Washington detected related signs in advance and had been monitoring the situation in real time.

A JCS official said the North, instead, had fired ship-to-ship missiles with a very short range, adding that it is impossible to fire cruise missiles from small vessels like the one used by Pyongyang.

Contrary to the North's claim that the missiles promptly hit their targets, the official said Seoul, through its monitoring equipment, detected that they in fact missed.

The North's state-run Korean Central News Agency reported that regime leader Kim Jong-un oversaw a test of strategic cruise missiles aboard a Navy warship in apparent response to the start of the South Korea-U.S. combined Ulchi Freedom Shield exercise on Monday.

The JCS said the military plans to thoroughly conduct the joint drills at highest levels under the combined defense posture, while keeping a readiness posture based on capabilities to overwhelmingly respond to any provocation by the North.