Defense Minister Tomomi Inada on Friday expressed displeasure with a recent U.S. parachuting drill at Kadena Air Base on Okinawa and said it might have flouted a bilateral accord.

Inada said U.S. parachute drop training should be “basically” conducted at an airfield on nearby Ie Island under a Japan-U.S. accord reached in 1996, and that the use of the U.S. Air Force base for parachuting training should be an exception.

“But the United States did not offer sufficient explanation on why the exercise conducted (Wednesday) amounted to an exceptional case,” Inada said at a regular news conference. “It is extremely deplorable that it took place at Kadena Air Base without Japan and the United States able to share the same perception in advance.

“The Japanese side does not think this was an exceptional case,” she added.

The U.S. military’s parachuting drill at the Kadena base was the second in just over two weeks despite local opposition and a request from the ministry’s regional bureau to suspend it.

According to the defense bureau in Okinawa, the U.S. military attributed the decision to unfavorable weather around the airfield on Ie Island. It was the first time that the bureau has confirmed the drill was held at night.

Residents remember an incident in 1965 in which an elementary school girl was fatally crushed by a trailer that had been airdropped to the village of Yomitan during a U.S. military drill.

The U.S. military previously conducted similar training at former Yomitan airfield, which was close to residential areas. But the villagers had strong concerns about safety, and Japan and the United States agreed in 1996 to relocate the drill to the auxiliary airfield on Ie Island.

The relocation of the drill led to the return of all of the land used for the Yomitan Auxiliary Airfield to Japanese control in 2006.