Crimes by US troops based on the southern Japanese island of Okinawa have long angered residents, who for decades have claimed the American military was out of control.

Tens of thousands of islanders rallied Sunday after anger was rekindled by the rape and murder of a 20-year-old woman in April.

A US civilian base worker -- a former Marine -- has been arrested. In a separate incident earlier this month a US sailor was detained after injuring two people in a drink-driving incident.

Statistics do not suggest a major problem with US military crime on the sub-tropical island. But the cases have fuelled persistent irritation at the intrusive American military presence on overcrowded Okinawa.

The island hosts about 26,000 US troops, more than half the total Washington keeps in all of Japan under a longstanding security treaty, and residents have long complained at the disproportionately heavy US footprint.

Okinawa was the scene of a bloody battle between Japan and the US in the waning months of World War II, followed by a 27-year American occupation that only ended in 1972 with its reversion to Japanese control.

The US military has gone all out to condemn the recent incidents and take measures to avoid further trouble, while the vast majority of its troops try to avoid the stigma created by their comrades who break the law.

Worried that more crimes could jeopardise the alliance, the military has been quick to express sympathy with Okinawans and taken steps to curtail problematic behaviour, such as restricting alcohol consumption and imposing a curfew.

"The overwhelming majority of American service members are law-abiding, upstanding members of this shared community," First Lieutenant George McArthur, a Marine public affairs officer, told AFP in a written response to questions.

"There is not an Okinawan and an American way to view horrific crimes -- only one view, and that is that we are all repulsed, angry and grieving together."

- 'Stomach turn' -

Troops have been instructed to stay away from the venue of Sunday's protest in the prefectural capital of Naha out of respect "and to prevent any possible conflict", McArthur said.

Most American personnel approached by AFP were reluctant to speak about the situation. If they did, they stuck mostly to talking points.

"We're doing everything we can to support the host nation," said a serviceman at an American-style off-base shopping mall in the beachside town of Chatan near the sprawling Kadena Air Force Base with his girlfriend.

Since the murder fewer troops are visiting the outdoor mall -- where shops, restaurants and bars have names like American Depot, Garage House, Camp Market and Outlet J. -- during evening hours, said Yoshie Morota, who runs a souvenir shop, though they still come during daytime.

"The crime made my stomach turn," Morota, 60, said of the rape and murder. "But it doesn't mean that all the Americans are bad."

She said around 30 service personnel picked up litter at a busy car parking area early Saturday at the complex and appeared to share a sense of grief with local residents.

In May the US military imposed a 30-day period of mourning, putting troops under curfew and banning the buying and consuming of alcohol off base.

Last year criminal cases suspected to be linked to the US military represented just 0.8 percent of all cases in Okinawa, according to figures from the prefectural government, remaining under one percent for the third year in a row.

But critics say high-profile incidents are likely to keep happening as the actual number of troops coming to Okinawa is larger than statistics suggest, given they regularly rotate through and tend to stay for a limited period.

"In reality, the number of perpetrators is huge," said Suzuyo Takazato, a female rights activist in Okinawa.

"Even if only one serviceman out of 100 commits a crime, it means 10 out of 1,000, and 100 out of 10,000, do," she added.