Japanese Prime Minister Sanae Takaichi said Monday that Japan strongly protests the alleged robbery and murder of a woman in the southernmost prefecture of Okinawa involving a US Marine.

Speaking to parliament in Tokyo on the first day of an extraordinary Diet session ahead of a policy speech, Takaichi said Japan has called for full US cooperation with the investigation and "strict discipline among US military personnel" to prevent a recurrence, Kyodo News reported.

On Monday, Devin Ballard, who was arrested over the alleged robbery and murder of local woman Anna Yagi, 39, at a hotel in the prefectural capital Naha in the early hours of Saturday, was sent to prosecutors, according to Okinawa police.

Okinawa residents have expressed outrage over the case after police on Sunday arrested the 20-year-old US Marine stationed in Okinawa on suspicion of murder and robbery.

Ballard has denied the allegations, police said.

Chief Cabinet Secretary Minoru Kihara said Monday that Japan will "continue to urge the US side to thoroughly enforce discipline."

On Sunday, Japanese Foreign Minister Toshimitsu Motegi and Defense Minister Shinjiro Koizumi summoned US Ambassador to Japan George Glass and commander of US Forces Japan Stephen Jost, respectively, to lodge strong protests, urging the US military to strengthen discipline and take thorough measures to prevent similar cases.

Crimes involving US military personnel stationed in Japan, including serious offenses such as murder, rape and robbery, have long been a source of deep public concern.

Official statistics show that Okinawa prefectural police recorded 101 criminal cases involving US military personnel, civilian employees and their family members in 2025, marking the first time the annual figure had exceeded 100 since 2003.