Japanese police are investigating claims a U.S. serviceman assaulted a boy on the island of Okinawa, where opposition to the U.S. military presence runs high.

Authorities say the serviceman allegedly broke into an apartment Friday and hit the 13-year-old boy in the face before jumping out a third floor window and suffering injuries.

Sources say the 24-year-old serviceman was intoxicated at the time. He was later hospitalized at a U.S. military facility.

Japan's Prime Minister Yoshihiko Noda called the alleged assault “deplorable,” noting it occurred while U.S. military personnel in Japan are under a nighttime curfew.

Japan summoned U.S. Ambassador John Roos, who later said he is “very upset” about the reported incident.

A U.S. military officer on the island, Colonel Brian McDaniel, said it is “extremely regrettable” when an alleged incident like this occurs.

The United States imposed a curfew for all military personnel in Japan two weeks ago following the arrest of two U.S. sailors for the alleged rape of an Okinawan woman.

More than 45,000 U.S. troops are stationed in Japan, about half of them on Okinawa.

Past crimes by U.S. military members on Okinawa have sparked mass demonstrations and calls for a reduction in the number of troops stationed there.

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