The Japanese government said Wednesday it has asked the U.S. military to swiftly report mishaps after it took six days for it to be notified that an F-15 fighter jet stationed in Okinawa had lost a part during a flight.

"It is truly regrettable that it was not reported immediately," said Chief Cabinet Secretary Yoshihide Suga, adding the government has asked the U.S. military to report such incidents promptly, investigate the cause and prevent a recurrence.

A part resembling an antenna weighing 1.4 kilograms fell from the fighter jet stationed at the U.S. Kadena Air Base in Japan's southwestern prefecture on Feb. 27, but Defense Minister Itsunori Onodera revealed the government was only notified on Monday.

"We would like to request the U.S. side to put top priority on confirming safety," Onodera told reporters in Tokyo.

The defense minister added that he received the information through the Foreign Ministry and not through the local defense bureau, which is the normal protocol, and said he was "baffled" by the unusual move.

The part was discovered to be missing after the fighter returned to base, according to a government source. So far, there is no report of injury.

Coming on the heels of a slew of similar incidents in recent months, the mishap drew fresh criticism from Okinawa, home to the bulk of U.S. military facilities in Japan.

"This is out of the blue. They are slow in providing information," said Deputy Okinawa Gov. Moritake Tomikawa.

Kadena town mayor Hiroshi Toyama also called for incidents such as this one to be disclosed immediately.

"We have been asking the U.S. military to prevent a recurrence every time there is a mishap, but they keep on happening," Toyama added.

In December, a window fell from a CH-53E transport helicopter onto the playground of an elementary school adjacent to the U.S. Marine Corps Air Station Futenma.

Last month, an F-16 fighter jet stationed at the U.S. Misawa Air Base in the northeastern Japan prefecture of Aomori dumped two fuel tanks in a lake due to an engine fire, forcing local fishermen to suspend fishing.