The incident is the latest in a string of sexual assaults by American servicemen to have angered the inhabitants of the southern Japanese prefecture, which plays reluctant host to dozens of American military bases.
Police arrested 27-year-old Sergeant Armando Valdez - who denies the assault - after the girl told her mother a drunken soldier had groped her and taken a photo of her naked chest in a car park in the city of Naha. The Okinawa Times, quoting police, said yesterday that Sgt Valdez still had the photograph of the girl in his mobile phone when he was questioned.
Okinawa's governor, Keiichi Inamine, who wants US troop numbers reduced on the island, called the alleged molestation "unforgivable" in yesterday's session of Okinawa's parliament, adding: "I can't help concluding there is a problem in the US military's discipline." Japan's senior spokesman, Hiroyuki Hosoda, called the incident "quite regrettable".
The military, which occupies almost a fifth of the main island of Okinawa including Kadena, the biggest and most active US Air Force base in east Asia, moved quickly to prevent the fallout from damaging the already strained ties with the residents.
"The type of behaviour alleged is completely unacceptable," said the commander of Kadena's 18th Wing, Brigadier-General Jan-Marc Jouas, who promised to co-operate fully with investigating authorities. But some islanders said the latest incident called for more radical solutions.
"There is a lot of anger in Okinawa right now," said Shoichi Chibana, an assemblyman who campaigns for the removal of American bases. "People are afraid of these crimes because they just never stop, and they won't stop until the military leaves."
More than 50,000 US military personnel and dependants, including 17,600 marines, are on Okinawa, which has a population of 1.3 million; the US military controls much of the land, sea and air.
In 1995, two marines and a sailor kidnapped and gang-raped a 12-year-old girl before leaving her for dead in a crime that capped years of sexual assaults and which caused the largest anti-US demonstrations since the end of the Second World War. Since then, the military has maintained an uneasy truce with islanders after agreeing to co-operate more closely with the Okinawa authorities in investigating crimes by its own personnel, and to return Futenma air base, which occupies 25 per cent of Okinawa's second city, Ginowan.
But tensions have recently returned. In May, thousands of demonstrators linked arms around Futenma to demand its closure, and a proposal to build a new base over a coral reef in a tiny fishing village has also brought protests which have continued for a year.
The tensions were further exacerbated last summer when a military helicopter crashed into the grounds of Okinawa university and Okinawa police were barred from inspecting the crash site.
"We are sitting on a tinderbox here," Mr Chibana said. "The military should leave."