The Defense Ministry has deployed Patriot PAC-3 antimissile air defense units to three Self-Defense Forces installations, in Tokyo and Chiba, to defend against possible North Korean missile strikes, Chief Cabinet Secretary Yoshihide Suga said Tuesday.

The PAC-3 units were deployed to the Defense Ministry’s headquarters in Ichigaya in Tokyo’s Shinjuku Ward, as well as the Ground Self-Defense Force’s Camp Asaka in Tokyo’s Nerima Ward and Camp Narashino in Funabashi, Chiba Prefecture, Suga told a news conference.

Those units have been deployed apparently to defend the ministry’s headquarters and key SDF units as well as the heart of the capital, given the limited range of the PAC-3 interceptors, which is about 30 km.

But Suga declined to reveal further details of the operation in order not to reveal confidential defense information.

“We’d like to refrain from explaining further because it would give away details of the cards we hold. At any rate, we have taken thorough measures to ensure the safety of the people,” Suga said.

Japan has already deployed Aegis destroyers in the Sea of Japan to monitor the possible launch of North Korean ballistic missiles, which Pyongyang has threatened to use to attack the United States, possibly including U.S. military bases in Japan.

Aegis destroyers are equipped with SM-3 interceptor missiles, which are designed to shoot down ballistic missiles in their early stage of flight. The Patriot PAC-3 systems are designed to intercept missiles that evaded the SM-3 defense layer.

On Monday, Suga told a news conference that Japan would use those antimissile systems only to defend Japanese territory.

Prime Minister Shinzo Abe has proposed that the government change its interpretation of the Constitution so Japan can intercept a ballistic missile fired at the United States, but an advisory panel to Abe is still discussing relevant issues and the government has maintained its current interpretation.

Shooting down a ballistic missile aimed at the U.S. would fall within the category of collective self-defense as defined by the United Nations Charter. The government interprets the war-renouncing Constitution as prohibiting the exercise of the right of collective defense.