US military personnel retrieve part of a fuel tank in the town of Fukaura

Japan's Defense Minister Nobuo Kishi described on Friday the US decision to resume F-16 fighter jet flights before the end of the investigation into fuel tanks drop by US aircraft as highly regrettable.

A US F-16 dropped two fuel tanks near residential areas in Aomori Prefecture during an emergency landing. This prompted Japan to make a representation to the United States, where it demanded the suspension of flights before the probe is completed. However, F-16 flights were recorded two days after the incident.

"This is highly regrettable," Kishi said at a press conference.

Aomori Governor Shingo Mimura raised the incident at the Aomori prefectural assembly on Dec. 1, where he said “I am taking this very seriously seeing as it involved a heavy volume of flammable fuel and the possibility of a major disaster.”

Defense Ministry sources said at the time that officials would call on their U.S. counterparts to ground all F-16 jets based at Misawa until their flight safety could be confirmed.

US F-16 fighters jets have dumped fuel tanks before in Japan, once in 2015 into the Sea of Japan, and another time in 2018, into a lake near the Misawa base.

Misawa hosts the airbase of the Japan Air Self-Defense Force and is also used by the US air force and navy.

Japan's Defense Ministry plans to ask the US once again to suspend F-16 flights until their "safety is confirmed."