The government held a ceremony on Thursday to mark the U.S. military's return of the largest tract of land in Okinawa in decades, despite last week's ditching of a U.S. MV-22 Osprey off the coast that rattled residents' nerves.

Okinawa Gov. Takeshi Onaga was absent from the event in the latest sign of strained ties between the local and central governments over disputes linked to U.S. base issues, including the use of the controversial Osprey tilt-rotor aircraft.

The return involved some 4,000 hectares of forest area, or roughly half the land used as the Northern Training Area on the main island, Okinawa. It was the biggest land transfer since the prefecture reverted to Japanese control in 1972 after being under U.S. occupation since the end of World War II.