U.S. military officials apologized Monday to an elementary school in Okinawa over a helicopter window that fell into its grounds last week and vowed they would do their best not to fly aircraft over the school.

No one was injured when the metal-framed window fell into the school near the U.S. Marine Corps Air Station Futenma last Wednesday in the city of Ginowan, but the incident has renewed local anger about the safety risks posed by the U.S. military presence on the island.

The U.S. military is set to soon announce the resumption of flights by the same CH-53E type of transport helicopter that caused the accident.

Col. Darin Clarke, who manages the Marines' government and external affairs in the Pacific, apologized to Futenma Daini Elementary School's principal Etsuko Kyan for causing great unease in the school and the wider region, according to the Ginowan education board.

Clarke told Kyan that safety checks of all CH-53E choppers as well as instructions to crew members have been completed, the board said. He also said the U.S. military have reconsidered flight rules at the Futenma base.

But Kyan said U.S. military aircraft should not be allowed to fly over school grounds, saying that as a person who is entrusted with lives of children she cannot be satisfied with the U.S. military just making utmost efforts not to fly over the elementary school.

Okinawa Deputy Gov. Moritake Tomikawa told reporters he has been notified by U.S. forces that they will announce Monday the plan to resume flights by the same type of aircraft. Tomikawa said Brig. Gen. Paul Rock, commanding general of Marine Corps installations in the Pacific, told him so on Sunday.

In Tokyo, Chief Cabinet Secretary Yoshihide Suga said, "Ensuring safety is most important. I would like to request the United States to give utmost considerations to safety and to minimize repercussions on local residents."

Okinawa Gov. Takeshi Onaga labeled the impending restart "truly ridiculous," while saying the central government was "incapable of being involved" as it failed to stop the flights, and describing the U.S. military as "not a good neighbor."

Defense Minister Itsunori Onodera said the government "has not received a sufficient explanation about (U.S.) measures to prevent a repeat (of the incident)."

U.S. officials have told the central and Okinawa governments that pilot error was behind the window's plunge.

This explanation has not satisfied locals in Okinawa, where tensions frequently flare over the island prefecture's disproportionate share of U.S. military facilities in Japan.

Parents of children at the affected school are among those unable to accept the resumption of flights so soon. Taking her 12-year-old son to the school, Tomoko Miyagi said the move is "unforgivable" and shows "contempt for the people of Okinawa."

The roughly 90-square-centimeter window weighing 7.7 kilograms dropped from a CH-53E transport helicopter and landed only a dozen meters away from where children were exercising.