Intercepting missiles not targeting Japan but flying over the archipelago would not violate the Constitution's ban on collective defense, sources at the Defense Agency said Sunday.

And needless to say, the country would be within its constitutional right to intercept a ballistic missile targeting Japan, the sources added.

The exercise of collective defense is officially interpreted as being banned by the Constitution. But the question of intercepting enemy missiles flying over Japanese territory has been much disputed within the context of the proposed introduction of a missile defense system.

According to the agency's conventional interpretation of the Constitution, the country is allowed to intercept missiles bound for Japan -- an act of self-defense.

The agency has made it known that the planned introduction of the missile defense system would not presume Japan's involvement in the defense of a third country.

This time, the agency apparently revised its interpretation to allow Japan to intercept a missile flying over the country bound for a third country, namely the U.S.

An agency source said the new interpretation is based on the premise that a missile flying over Japan might pose a threat if it accidentally came down in the archipelago.

The source said, however, that the Constitution would still ban Japan from intercepting a missile that does not fly over the country, even if it is targeted at the U.S.

Under the new interpretation, Japan can launch missiles from Maritime Self-Defense Force warships equipped with the Aegis air-defense system against North Korean ballistic missiles heading for Hawaii or Guam, for instance, if the missiles fly over northern or western Japan, the sources said.