A US serviceman stationed in Japan's southern island of Okinawa has been arrested on suspicion of raping a woman, Japanese police say.
The arrest will likely add to complications for a controversial plan to relocate the US airbase on the island.
The government in Tokyo and authorities in Okinawa have long been at loggerheads over the relocation of the US Marines' Futenma airbase, which is in an urban area of the southern island.
The Japanese government accepted a court-mediated settlement plan this month to resume talks with Okinawa authorities, who want the base off the island altogether.
Okinawa police arrested a 24-year-old sailor stationed at the camp for allegedly raping a woman in her 40s at a local hotel.
"We promptly told the US side this is extremely regrettable and demanded firmly stricter discipline and prevention of recurrence," Chief Cabinet Secretary Yoshihide Suga said.
Okinawa, the site of a bloody World War Two land battle, hosts the bulk of US military forces in Japan, and many residents resent what they see as an unfair burden.
US installations take up about 18 percent of Okinawa's land.
In 1995, a 12-year-old Japanese schoolgirl was raped by three US servicemen on Okinawa, sparking huge protests. There have been several other crimes committed by US service members serving on the Japanese island that have fuelled locals' anger.