TOKYO — An American sailor’s arrest in an alleged rape on Okinawa was “extremely regrettable,” Japan’s top government spokesman said Monday about a case that renewed ill feelings on the southern island that sees the U.S. military presence there as a heavy and unfair burden.

Chief Cabinet Secretary Yoshihide Suga said the government protested to Washington hours after the arrest Sunday and demanded it tighten discipline among U.S. personnel and take steps to prevent similar problems.

Okinawa police arrested Justin Castellanos, 24, a U.S. Navy seaman at Camp Schwab on Sunday. Police say he is suspected of sexually assaulting a Japanese tourist in her 40s as she slept at her hotel earlier that morning. Castellanos has not been formally charged.

Phone calls to U.S. Navy’s public affairs office in Japan were not answered.

Kyodo News agency said the woman was sleeping in the hallway, and the sailor allegedly dragged her into his room and raped her.

Okinawa Gov. Takeshi Onaga told reporters that the case is “a serious crime and blatant violation to women’s human rights.” He also said since the woman was a tourist, the alleged attack could scare off visitors to Okinawa, where tourism is a key part of the economy.

About half of the 50,000 American troops in Japan are based in Okinawa, and its residents complain about noise and crime from the bases. Sex crimes are particularly sensitive issue on the island.

A 1995 rape of a schoolgirl by three U.S. servicemen sparked an outcry, eventually leading to an agreement to relocate the Marine Corps Air Station Futenma to a less crowded part of the island, though the plan has stalled since because many residents want it entirely moved outside Okinawa.