Japan and the United States have been stepping up efforts to build a joint missile defense system following North Korea's nuclear test in October.
Australia would join the two countries to share information on missile defense and discuss how to respond to various situations, the Japanese business newspaper Nikkei reported, citing unidentified officials at Japan's Defense Ministry.
The three countries reached an agreement on the joint study during a meeting of senior defense and foreign affairs officials in Tokyo last month, the newspaper said.
However, a Defense Ministry official said nothing had been decided. The official, who spoke on condition of anonymity citing ministry practice, refused to confirm whether the three countries were in talks on such an arrangement.
In Australia, Defense Minister Brendan Nelson's spokesman, Nigel Blunden, declined to comment on the report.
The newspaper said the three countries would explore scenarios of possible attacks by North Korean medium-range missiles as well as Chinese ballistic missiles reaching the U.S. territory of Guam or Australia.
Australia has not decided to introduce a missile defense system but is expected to explore the possibility of having such a system, the report said.
Japan is acquiring both land-based Patriot PAC-3 and sea-based Standard SM-3 missile defense systems. The SM-3 missiles are to be deployed aboard four Japanese Aegis-equipped air-warfare destroyers (AWDs) from around 2011.
Australia and Japan signed a security agreement in March that enables Japanese forces to train alongside Australians for disaster relief and peacekeeping missions and boosts cooperation between the two countries in counterterrorism and intelligence sharing.
Australia also is in the process of acquiring three advanced AWDs equipped with the Aegis missile guidance system. Should the government choose, they could also be equipped with SM-3 missiles.
During a visit to Australia earlier this month, the U.S. naval commander in Japan, Rear Adm. James Kelly, said Aegis was the foundation of an anti-missile capability and the U.S. Navy was moving toward a surface combatant force primarily equipped with Aegis warships.
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