The government has lodged a protest with the United States over the alleged rape of a Japanese tourist by a U.S. sailor in Okinawa on Sunday.

Justin Castellanos, 24, of the U.S. Navy’s Camp Schwab in the prefecture, is suspected of raping a woman in her 40s at a hotel in Naha where they were both staying.

“It was extremely regrettable that this case happened,” Chief Cabinet Secretary Yoshihide Suga told a news conference. The government demanded that the United States “tighten discipline and prevent a recurrence of such incidents,” he said.

Suga quoted U.S. officials as saying they are taking the case seriously. He added, it would be “regrettable” if a U.S. serviceman is found to be guilty.

The government’s top spokesman said the Foreign and Defense ministries filed a protest Sunday afternoon with the U.S. Embassy and with U.S. forces stationed in Japan.

Speaking to reporters Monday in the Okinawa prefectural capital of Naha, Gov. Takeshi Onaga condemned the incident.

“It was a serious crime in violation of women’s human rights and can never be tolerated,” Onaga said. “I feel strong resentment.”

Citing the fact that the woman is a tourist from Fukuoka Prefecture, Onaga said the incident “might pose a significant impact on tourism, a major industry for the prefecture.”

On Sunday, local police arrested Castellanos on suspicion of taking the woman to his room at the hotel and raping her there. He denies it.

Police said the suspect took the woman to his room after finding her sleeping in the corridor.

The sailor and the woman were both staying at the hotel but were unacquainted, they said.

Crimes by U.S. military personnel have caused concern and protests in Okinawa, which hosts the bulk of U.S. forces in Japan.