(CNN) -- Investigators in Japan are investigating a second reported sexual assault connected to the U.S. military, police said Thursday.
Japanese protesters shout slogans last week in front of a U.S. camp on the southern Japanese island of Okinawa.
Investigators said they are looking into allegations that a member of the U.S. Army raped a Filipino woman on the island of Okinawa.
Last week, police detained a U.S. Marine in the alleged rape of a 14-year-old girl on Okinawa -- a case that has stirred outrage across Japan.
It was not immediately clear whether the suspect in the second case was a soldier or a civilian employee at the military's sprawling base in southern Japan, where tens of thousands of troops are based.
The U.S. Army said commanders are aware of the second allegation and are looking into it.
In the first case, police said they had detained 38-year-old Tyrone Luther Hadnott.
Prime Minister Yasuo Fukuda condemned the alleged incident as "unforgivable," and the U.S. military confined troops to their bases or off-base homes for "a period of reflection" as of Wednesday morning, except for work, worship, school or medical appointments, according to a news release from Camp Butler on Okinawa.
"This period of reflection will allow commanders and all service members an opportunity to further review procedures and orders that govern the discipline and conduct of all U.S. service members serving in Okinawa," the release said.
The military did not indicate how long the restrictions -- which began at 7:30 a.m. Wednesday -- would remain in effect.
The U.S. military said it formed a sexual assault prevention task force after the incident.
Similar cases have strained relations between the United States and Japan in the past.
Anti-U.S. sentiments boiled over in 1995 after a 12-year-old Okinawan schoolgirl was gang-raped by three American servicemen.
Two years ago, a U.S. civilian military employee was jailed for nine years for raping two women. E-mail to a friend
CNN's Junko Ogrua contributed to this report.
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