The two sailors were arrested Tuesday over the alleged rape of a woman in Okinawa, home to most of the U.S. military bases in Japan, and where there is much public resentment against the U.S. military presence.
After Japan lodged its protest with the United States, Okinawa Gov. Hirokazu Nakaima met with Japanese Defense Minister Satoshi Morimoto, calling the alleged incident "madness," and demanded the U.S. government cooperate in the investigation and impose stricter discipline, Kyodo News Agency reported.
The Wall Street Journal quoted U.S. and Okinawa officials as saying the two U.S. sailors were from a visiting naval ship. They have been accused of attacking and raping a 27-year-old Okinawa woman early Tuesday as she was returning home from work.
Police say the woman suffered a neck injury during the attack.
A U.S. Embassy statement said Ambassador John Ross was "extremely concerned" by the allegations and promised the U.S. government would fully cooperate with Japanese authorities in the investigation.
The Journal said the incident threatens to strain the United States' bilateral military cooperation with its main Asian ally and comes at a time when Japan is wrapped up in territorial island disputes with China and its neighbors.