A small cylindrical object fell onto the roof of a nursery school in Okinawa Prefecture as a U.S. military plane flew overhead on Thursday, local officials said.

There were no reports of injuries from the incident, which occurred at around 10:20 a.m. in the city of Ginowan — home to a U.S. Marine Corps air base involved in a contentious relocation plan. The nursery school is located about 300 meters from the base.

Okinawa Gov. Takeshi Onaga, a staunch opponent of the plan to relocate the base within his prefecture, said it would be “outrageous” if the object, measuring about 15 centimeters, indeed came from a U.S. military plane. Local officials were seeking to identify the object.

According to the nursery school, about 50 children were playing on its grounds while eight toddlers and two caregivers were inside the building when they heard a loud noise.

“I’m appalled to think what would have happened if the (impact point) had shifted just a little bit,” said Take Nago, the 78-year-old chief caregiver at the facility.

The latest case adds to existing concerns of local residents over safety. In mid-October, the U.S. Marines resumed flight operations of its CH-53E transport helicopters, insisting it has confirmed their safety following a crash-landing by one a week before.

In the accident, the large transport helicopter burst into flames as it made an emergency landing near the U.S. military’s Northern Training Area on the main island of Okinawa.

None of the seven crew members or local residents was hurt in the accident. But the site, in the village of Higashi, was a few hundred meters away from homes, rekindling concerns over the risks faced by locals who live close to U.S. military facilities.

A plan by the U.S. and Japanese governments to relocate U.S. Marine Corps Air Station Futenma, located in the city, to the northern part of the Okinawa main island has met with strong local opposition.

The bulk of U.S. military facilities in Japan is concentrated in the prefecture.