Local officials in Okinawa are voicing concern after an apparent bullet damaged a shed near a US base in that prefecture.
On Thursday, police received a report from the owner of a farm shed in Nago City that the glass in its windows had been broken and what looked like a bullet was found inside.
The object measured 1 centimeter in diameter and 5 centimeters in length. Nobody is known to have been injured.
Okinawa Prefecture has been informed of a live fire exercise that began on Monday at the adjacent US Camp Schwab.
Police are studying the object and will lodge inquiries with the US military over the possibility that it could be a stray round from the exercise.
The shed owner said the damage to the glass shows that something small pierced it at high speed and added that a concrete block wall along the suspected trajectory had also been hit.
The Okinawa Prefectural Government says bullets have been found near US bases in at least 28 instances since reversion to Japan from US military rule in 1972. In 2002, a bullet landed in front of a man who was working at a farm in Nago City.
Okinawa's Vice Governor Kiichiro Jahana says he is waiting for the outcome of the police investigation. He added that if the object is indeed a bullet fired by US troops, he could not help feeling angry.