Two US servicemen were arrested Tuesday on suspicion of gang-raping a Japanese woman in Okinawa, reports said, as anti-American feeling runs high on the strategically vital island.
The incident comes amid swelling protests over the recent deployment on the island of 12 Osprey transport aircraft, with the plane's perceived poor safety sparking concern among local residents.
National broadcaster NHK said the two men, both 23 years old, had been arrested over the alleged assault of the woman before dawn on Tuesday.
One of sailors admitted carrying out the attack, but the other has denied it, according to TV Asahi.
A spokesman for the Okinawa prefectural police refused to comment on the reports.
The incident has the potential to snowball, feeding in to the increasingly vociferous anti-base movement.
Previous attacks have generated huge outpourings of anger.
The gang rape of a 12-year-old Okinawan girl by US servicemen in 1995 sparked mass protests resulting in a US-Japan agreement to reduce the huge US military presence on the Okinawan chain.
But the agreement has been bogged down for years over plans to relocate the Futenma US marine airbase, which currently sits in a crowded urban area, to a coastal zone.
Islanders want to see the airbase moved off the island chain and insist the rest of Japan should shoulder more of the burden of the US presence.
Okinawa is a reluctant host to around half of the 47,000 US military personnel stationed in Japan.
In September tens of thousands of people rallied against deployment of the tilt-rotor Osprey, which can take off and land like a helicopter and fly like a plane.
A number of crashes involving the aircraft sparked safety fears, but commentators say the Osprey is a proxy issue for a people who are fed up of the huge US presence.
Washington sees the island as a vital strategic base in a region that is increasingly seeing the power of China's rising military.