On Wednesday morning, an angular object roughly 3ft (1 meter) across fell onto a sports field packed with elementary school children near the Futenma US military base in the Japanese prefecture of Okinawa. The object was discovered to be a helicopter window, complete with the frame, that had fallen off an American CH-53 aircraft flying above the school grounds.

READ MORE: US Marine chopper reportedly drops object on Okinawa nursery during flyover

One 10-year-old boy, out of some 50 children who were assembled in the sports field, was slightly injured in the incident, Reuters reports, citing a prefecture official. The exact cause of his injuries was unclear.

The US Marines have admitted helicopter window fell on a children's sports ground, but have not clarified exactly how it happened.

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