The US military flew its helicopters over a school in Okinawa, Japan on a day when the institution held an evacuation drill for the students and staff. Needless to say, chaos ensued as the students' parents and Japanese authorities were outraged by the manoeuvres.

Even as the US forces already face a string of criticisms in the Japanese soil, the latest development surfaces and it is bound to ruffle the Japanese feathers. Tokyo officials have already sought an explanation from the US personnel over the incident.

Initially, the US forces denied such overflight taking place above a local school but Japan's Defense Minister Itsunori Onodera released video evidence of the flights. Cameras installed at the school, located close to the Futenma base in Japan's southern island of Okinawa, captured the movement of AH-1 attack helicopters and one multipurpose UH-1 helicopter in formation shortly after noon on 18 January, Thursday.

"We have confirmed the flights over the school with the camera footage and visual checks by ministry surveyors," said Onodera. "It is unacceptable. We would like the US to deal with this."

While Okinawa's Governor Takeshi Onaga called the flight "completely outrageous," Japan's Chief Cabinet Secretary Yoshihide Suga said: "It's deplorable that this has happened even though we've requested firmly that the US not fly above the school."

Incidentally, the school was also carrying out emergency drills, which added fuel to the tensions. "To fly (helicopters) over the school the same day they start the drills – just what is the US military thinking? I just can't believe it. I can't accept it," a mother, who's two children goes to the school, told the local daily Mainichi Japan.

Another parent said: "The evacuation drills were just for good measure, but if they continue to fly over the school, then that changes the conversation entirely. If something doesn't change, then the anxiety won't fade and reopening the grounds will be impossible."

The US' Okinawa military base, which hosts about 25,000 troops, has been a source of tension for several years, with anti-military sentiment running high among the islanders. Since the island is strategically located at the edge of the East China Sea, it gives the US an enormous advantage to have an installation in Okinawa to handle its operations in the sensitive region.

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Marines of the US Marine Corps, based in Japan's Okinawa, take part in a practice Lee Jae Won/Reuters