Authorities in Okinawa issued a protest to Japan's central government on Wednesday after U.S. forces conducted parachute drop training the previous night at Kadena Air Base on the prefecture's main island, despite a bilateral agreement that such drills should be held on a remote island.

The parachute drop conducted by U.S. forces at the Kadena base on Tuesday night was the fourth such exercise this year, despite a 1996 bilateral agreement that stipulates such training be carried out on Ie Island in the prefecture.

"We cannot help but feel strong resentment because the Kadena base has been continuously used for (parachute) training," said Deputy Okinawa Gov. Kiichiro Jahana in a meeting with Foreign and Defense ministry officials at the prefectural government building. "There has been growing mistrust among people in Okinawa."