Japan has failed to track the trajectory of some of North Korea's new types of short-range missiles in a recent series of launches, raising concerns over Tokyo's defense capabilities, sources close to the matter have said.

The missiles, including some capable of reaching Japan, apparently escaped detection due to their low altitudes and irregular trajectories, and Tokyo is said to believe that North Korea is attempting to break through Japan's existing missile defense network.

The government is increasingly concerned that the North is making progress in its technological developments. It is considering operating two or more Aegis-equipped destroyers to cover low altitudes as well as strengthening its radar functions, the sources said Sunday.