South Korea, the U.S. and Japan have recently enhanced their surveillance of Pyongyang's missile activities after detecting signs of a possible missile launch by North Korea. 
 
A government source in Seoul said on Tuesday that South Korea strengthened its missile defense surveillance after signs that are usually observed before missile launches were recently detected from North Korea's missile base.
 
Signs were reportedly detected on Monday that the North activated its radar which tracks missile trajectories, and communication activities within the North's missile base surged.
 
The U.S. and Japan are known to have detected similar signs as well and shared the information with South Korea.