Japanese police have arrested a US Marine on suspicion of murder and robbery in Okinawa. The arrest has triggered a diplomatic protest from Japan’s prime minister.

Devin J. Ballard, a 20-year-old lance corporal, was arrested on October 4. He is stationed at Marine Corps Air Station Futenma as part of the III Marine Expeditionary Force. Police allege he killed Anna Yagi, 39, in a hotel room in Naha on October 3. He has denied the allegations.

Prime Minister Sanae Takaichi called the incident extremely brutal and heinous. She said Japan had lodged a strong protest with the United States. She demanded full cooperation with the investigation, strict discipline among US personnel, and measures to prevent recurrence.

Foreign Minister Toshimitsu Motegi summoned US Ambassador George Glass over the case. The US Embassy in Tokyo said it was cooperating with Japanese authorities and extended condolences to the victim’s family.

Most of the 18,000 Japan-based Marines are stationed in Okinawa. Their presence has long stirred resentment over noise, aircraft accidents and the conduct of personnel. The killing could complicate efforts to relocate Marines from the busy Futenma base to Henoko.