The US presence on Okinawa in southern Japan is a key part of the security alliance between the two countries. The base houses about 26,000 US troops.
There are plans to relocate part of it to a less-populated area of the island, but many Okinawans want the air base removed altogether.
They object to the alleged crimes and accidents attributed to the troops. Resentment at the US presence has been growing among many locals, particularly since the 1995 gang-rape of a 12-year-old girl by US troops.
In 2016, the murder of a woman was linked to an ex-Marine employed at one of the bases, also leading to a temporary ban on alcohol as well as a midnight curfew.
