A US Marine was arrested Sunday on suspicion of murder and robbery after a woman was found dead in a hotel room in Japan, leading the country’s prime minister to condemn the alleged crime as “extremely brutal and heinous.”

The 39-year-old woman was discovered unconscious in her hotel room in Naha, on Okinawa island, early Saturday and was pronounced dead at the scene, according to Okinawa police.

“The Government of Japan has strongly protested to the U.S. side and has called for the fullest possible cooperation with the investigation, thorough discipline among U.S. military personnel, and comprehensive measures to prevent the recurrence of crimes and accidents,” Prime Minister Sanae Takaichi said in a statement.

Police said the condition of the woman’s body indicated that she may have been killed, though they did not release further details about the case.

The suspect, a 20-year-old Marine, was assigned to Futenma Air Station on Okinawa, police said.

Security camera footage reportedly showed a shaved-headed man, believed to be a foreign national, entering the hotel room with the woman before later leaving the building carrying her belongings, according to police.

In a statement, the US Marine Corps offered its condolences to the victim’s family and said it treats the allegations “very seriously” and expects Marines to meet the highest standards of conduct.

“We are actively cooperating with Japanese authorities in response to allegations of serious criminal actions by a Marine assigned to the III Marine Expeditionary Force,” the statement said.

The US Embassy in Tokyo said it was aware that an American service member had been taken into custody after the death of a Japanese national in Okinawa.

“As an investigation is underway to determine the facts of the case, the United States is communicating and cooperating with the Government of Japan and local authorities,” the embassy said.

The woman’s body was found at about 4:30 a.m. local time Saturday. The Marine was arrested less than a day later, at around 1 a.m., while walking through the city, police said.

Authorities said the investigation remains ongoing.

Although Okinawa plays a major role in US military strategy, the presence of American forces on the island has periodically fueled frustration and resentment among local residents.

In 1995, the rape of a 12-year-old girl by three US servicemen triggered widespread anger and large protests across Okinawa.