An Air Self-Defense Force panel began a full investigation Tuesday after an F-4 fighter accidentally fired nearly 200 cannon rounds into civilian areas during a ground attack drill Monday over western Hokkaido.

Self-Defense Forces members search a golf course for 20mm practice shells fired by mistake by an Air Self-Defense Force jet.

The panel is questioning the 32-year-old pilot of the jet to determine whether the cannon was fired through pilot error or a malfunction of the aircraft's electrical system, ASDF officials said.

The pilot, who has about 2,100 flying hours, has told investigators that safety measures aboard the aircraft were apparently in order.

The fighter fired 188 rounds from its 20mm high-speed cannon by mistake while flying over Eniwa, western Hokkaido, shortly before 11 a.m. Monday, initial reports said. No one on the ground was injured.