Japanese version of the American Aegis Ashore land-based missile interceptor systems will not be equipped with Cooperative Engagement Capability (CEC) meant for air defense.
The Aegis Ashore units are likely to be deployed in Akita and Yamaguchi prefectures facing the Sea of Japan, which separates the country from Korean peninsula.
"Japanese version of the Aegis Ashore system will thus be designed solely for defense against ballistic missiles, not capable of defense against warplanes or cruise missiles," Japan Times quoted sources as saying.
The CEC equipment enables early-warning planes, Aegis destroyers and others to share positional data on enemy aircraft, cruise missiles and other targets of interception, leading to greater interceptor ranges and quicker responses to threats.
"Installing the CEC equipment may be considered in the future as it is a desirable feature, but there is no plan to do it at the moment," a second source said.
"CEC equipment would cause additional costs of tens of billions of yen," according to another source, which could have discouraged Japan from adopting equipment.
A US military source questioned the Japanese plan to restrict themselves to Ballistic missiles and suggested strengthening its air defences to be prepared against threat from China and Korean peninsula.
Japanese Defense Ministry recently revised its estimate of the introduction costs from about ¥80 billion per unit to ¥134 billion. The budget is likely to go up owing to the purchase of sophisticated Lockheed Martin solid-state radar equipment for the Aegis Ashore units.