According to local police and the US command, on Sunday evening, the intruder cut through the protective net at the US Marine Corps base's perimeter and sneaked in.
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Then he blew up an unknown number of gas canisters on the second floor of a building, at the door of the Japanese defence bureau's office at the military base.
No one was injured in the explosion. The total value of the property damage done has yet to be estimated. The police are looking for the suspect.
Camp Foster houses the headquarters of the Butler Marine Corps and its facilities.
Okinawa, an island prefecture which accounts for a small fraction of Japan's territory, is home to 74 percent of US military facilities in the country and more than half of all US forces deployed in Japan.