TOKYO (AP): Japan deployed its third advanced missile interceptor system Wednesday, just south of Tokyo near a major naval base, a defense official said.

Air Self-Defense Forces personnel installed the land-based Patriot Advanced Capability-3 system at the Takeyama base in Yokosuka, just southwest of Tokyo, a Defense Ministry official said on condition of anonymity because of ministry policy.

Yokosuka is the site of Japan's largest naval base and the homeport of the U.S. Seventh Fleet.

The system includes an unspecified number of launchers, a special vehicle equipped with radar and another that serves as a control station. PAC-3 systems were installed at two other bases near Tokyo last year.

Japan has been rapidly augmenting its missile defense amid concerns over possible threats from North Korea. It plans to deploy the PAC-3 defense system at eight more bases across the country by March 2011.

The fourth PAC-3 system will be deployed at Kasumigaura in Ibaraki by the end of March, the ministry official said. The first four are mainly aimed at defending the capital region.

The Defense Ministry also conducted an initial study in the Tokyo region this month to determine the best locations for the deployment of anti-ballistic missiles to defend the capital.

The PAC-3 units are too remotely deployed to defend the capital and will have to be brought into Tokyo in case of a possible attack.

The surface-to-air Patriots would be used as a last defense in case interceptors fired from U.S. or Japanese warships fail to knock out incoming missiles.

To step up its naval defense capability, Japan also plans to begin installing Standard Missile-3 interceptors on its destroyers over the next few years. In December, Japan successfully test-fired its first SM-3 from an Aegis radar-equipped destroyer off Hawaii.

Tokyo and Washington have stepped up their joint missile defense capabilities. In February, the U.S. military deployed PAC-3 at a base on the southern Japanese island of Okinawa, where most of the roughly 50,000 American troops in the country are based.