A U.S. Army serviceman is under investigation for allegedly sexually assaulting a Philippine woman in the southern Japanese island of Okinawa, the U.S. military and Japanese officials said Thursday.

The investigation, apparently at the preliminary stages, was disclosed amid a rising furor over a recent series of crimes blamed on American troops, including the arrest last week of a Marine on suspicion of raping a 14-year-old.

Details in the latest case were hazy, but it involved an alleged attack at an Okinawa hotel earlier this month, officials said. A report by Japan's Kyodo News agency said American military authorities had taken the servicemen into custody.

"They are investigating charges of that," said Sgt. Terence Peck of U.S. Forces Japan. He refused to provide additional details, referring calls to the U.S. Army.

The woman, also unidentified, was taken to a hospital following the alleged attack after meeting with a serviceman in a hotel, said Takashi Ariyoshi of the Japanese Foreign Ministry. Okinawa police refused to provide further details.

The U.S. military on Wednesday imposed tight restrictions on U.S. troops in Japan to crack down on the crime spree, limiting some 45,000 military personnel, civilian employees and their families to bases, workplaces or off-base homes indefinitely.