TOKYO and LONDON -- The III Marine Expeditionary Force in Japan confirmed on Monday that Devin Jacob Ballard, 20, a Marine lance corporal, was the service member arrested on Sunday on suspicion of murdering a Japanese woman in a city near a U.S. base.

Ballard is assigned to the III MEF, a spokesperson told ABC News, adding that the force would not release further personal or administrative details "to protect the integrity of the ongoing investigation and adhere to privacy regulations."

Asked whether the arrest has prompted any additional measures, including changes to liberty or personnel restrictions, 1st Lt. Tyler N. Thomas, media engagement officer for the III MEF, told ABC News, "All U.S. service members in Japan are subject to strict off-duty conduct and liberty guidelines."

"While we continuously review our security posture and force discipline, we have no announcements regarding changes to liberty policies at this time," Thomas added.

Ballard, who was named on Sunday by the Japanese media, was arrested on Sunday after the woman's body was found early on Saturday in Naha, the capital city of the Okinawa prefecture. Police identified the deceased as Anna Yagi, 39, saying she was pronounced dead at the scene after being found at about 4:30 a.m. on Saturday.

Ballard was arrested on suspicion of murder and robbery. Police found Anna Yagi’s backpack near the hotel with her wallet still inside. Surveillance video indicates the suspect left the scene on foot.

Investigators are examining Ballard’s movements before and after the incident and the nature of his relationship with Yagi.

Japanese officials lodged what they described as a "strong" protest against the United States on Sunday, as word of the apparent killing spread.

"The occurrence of such an extremely brutal and heinous incident is a matter of profound regret, and as the Government of Japan, we have lodged a strong protest with the U.S. side," Japanese Prime Minister Sanae Takaichi said on Sunday.

Shinjiro Koizumi, the Japanese minister of defense, said late on Sunday that his office summoned local U.S. military leaders to convey "Japan's extremely serious concern regarding the robbery and murder incident that occurred in Naha City, Okinawa Prefecture, while strongly protesting to the U.S. side."

When asked whether the case could fuel distrust of the U.S.- Japan alliance, Koizumi said the incident must not be allowed to shake public confidence in that alliance, including among Okinawa residents.

The United States has more than 50,000 soldiers, sailors, airmen and Marines stationed throughout Japan, including on several bases in Okinawa, an island chain in the south. Okinawa hosts a large share of the U.S. military presence in Japan and remained under U.S. administration until its 1972 reversion to Japan.

Ballard's force, the III Marine Expeditionary Force, said on Sunday that it was "actively cooperating with Japanese authorities," adding, "We extend our deepest condolences to the victim’s family and friends."

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