Japan tested a ballistic missile defense unit in the center of Tokyo on Tuesday, stepping up preparations to secure the capital from what it sees as an increased threat from neighboring North Korea.

The exercise at the Defense Ministry headquarters was designed to test the troops’ ability to use the equipment, a ministry spokeswoman said on condition of anonymity, citing department policy.

The soldiers did not test-fire actual missiles, she said. She said no further details could be released because of national security concerns.

The drill involved land-to-air PAC-3 interceptors, Defense Minister Shigeru Ishiba told reporters.

“We are not deploying PAC-3 just for fun,” he said. “We have to make sure its capability is truly reliable and the personnel in charge of it are well trained.”

Japan has been aggressively augmenting its missile defense capabilities through joint programs with the U.S. amid concerns about a possible threat from North Korea.

The North has missiles that can reach any target in Japan, where roughly 50,000 American troops are based under a mutual security pact.

About 250 Ground Self-Defense Forces soldiers participated in the event, the first full-fledged exercise using the PAC-3 unit which Japan deployed last year to demonstrate.

Tokyo and Washington have accelerated a joint missile defense program following North Korea’s missile and nuclear tests in 2006.

Japan has deployed four PAC-3 missile defense units _ each including several launchers, a radar vehicle and a control station _ around Tokyo. Japan plans to deploy the units at several more bases by March 2011.

Japan will also conduct its first test-firing of the PAC-3 interceptor at White sands Missile Range in New Mexico in September.

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.