The Japanese government on Friday doubled-down on its accusation that the U.S. Marine Corps flaunted safety concerns by flying helicopters above a school near a U.S. air base in Okinawa, despite U.S. military denials.

"As you can see from the video footage (we have), the helicopters' underbellies are clearly visible as they flew," Defense Minister Itsunori Onodera said, referring to video shot from a school which had a helicopter window fall into its grounds on Dec. 13, sparking outrage from school authorities, parents and political figures.

(Video) U.S. choppers fly over Okinawa school despite promise to avoid it: Japan

"Children, teachers and parents will certainly be worried. This is a kind of flight we don't want to see," the minister said. Onodera also said he will continue to urge the U.S. military to avoid flying over the school just outside the Marine Corps Air Station Futenma.

Okinawa Gov. Takeshi Onaga also expressed strong disappointment over what he sees as a "broken promise" that the U.S. military would avoid flying over the school as much as possible since the December incident.

"It is completely outrageous," Onaga said at a press conference.

Local concerns are deepening over continuing accidents and mishaps involving U.S. aircraft in the southern Japanese island prefecture where the bulk of U.S. military forces in Japan are stationed.

The Okinawa prefectural assembly on Friday adopted documents demanding the suspension of the operation of the Futenma base by February next year, and the removal of the Marines from the prefecture, as many of the incident-prone aircraft fly out of the base.

The Dec. 13 incident at the Futenma No. 2 Elementary School also involved a Futenma-stationed CH-53E large transport helicopter. Nobody was injured, but locals were incensed as the window, weighing 7.7 kilograms, landed only meters from where more than 50 children were taking part in physical education activities.

After the incident, the U.S. Marine Corps in Okinawa said it instructed all crew of aircraft taking off and landing at the Futenma base to avoid flying over schools to the "greatest extent possible," according to the Japanese Defense Ministry.

The ministry, for its part, has installed security cameras at the school and sent local defense bureau officials to watch for any U.S. military aircraft flying over.

On Thursday afternoon, cameras and defense officials spotted two AH-1 attack helicopters and one UH-1 multipurpose helicopter flying over the school, according to the ministry, prompting it to lodge an immediate protest.

Onodera said Friday that the ministry has asked the U.S. military to again confirm the circumstances of the flights using video footage shot from its cameras placed at the school.

No children were in the playground when the three helicopters passed over, but not long before, students had been evacuated from the area during a drill being carried out in response to the window incident.