North Korea fired multiple unidentified cruise missiles toward the Yellow Sea at around 7 a.m. Tuesday, which are being analyzed by intelligence authorities in South Korea and the U.S.

According to South Korea's Joint Chiefs of Staff(JCS), it has bolstered surveillance and vigilance, and is coordinating closely with the U.S. while closely monitoring developments in the North.

This comes just two days after Pyongyang's previous firings of the new strategic "Pulhwasal-3-31" cruise missile on Sunday, which followed an inaugural test-firing last Wednesday.

Military officials in Seoul assume that the North fired additional Pulhwasal-3-31 missiles from near the capital Pyongyang on Tuesday. It is believed to have a maximum range of two-thousand kilometers.

The JCS speculates that the regime is conducting a series of launches in a short period of time in a bid to improve the performance of the new strategic missile, presumed to be capable of carrying a nuclear warhead and launchable from land as well as both above and below the sea.