US President Barack Obama (L) and Japanese Prime Minister Shinzo Abe walk as they participate a tree planting ceremony during a visit the Ise Grand Shrine in Ise, Mie Prefecture, Japan, May 26, 2016, as part of the G7 summit meetings. [Photo/Agencies]

ISE, Japan - US President Barack Obama extended "sincerest condolences and deepest regrets" over the murder of a Japanese woman by a US military-affiliated civilian here late Wednesday at a meeting with Japanese Prime Minister Shinzo Abe.

Responding to a strong statement of protest from the Japanese prime minister, Obama said the murder was a "tragedy" and considered "inexcusable", and pledged to continue to cooperate fully with the investigation to ensure that justice is done under the Japanese justice system.

The 20-year-old victim was raped and strangled by a former US Marine in Japan's Okinawa Prefecture last month, whose body was dumped in a forested area.

At the meeting, Abe raised a formal protest over the tragic death, saying that he felt profound resentment for this self-centered and despicable crime. He also urged the United States to take effective measures to prevent similar incidents from happening again, according to a press conference after the talk.

The Okinawa murder has triggered a surge in strong protest and anti-US sentiment in the Japanese southernmost prefecture, prompting the meeting between the two leaders, which was originally slated for Thursday, to be rescheduled and held only hours after Obama's arrival.

Some 4,000 people in Okinawa, including National Diet members, rallied in front of the US Kadena Air Base on Wednesday, protesting against the murder of the innocent young woman, as well as demanding scaling down US bases and revising the Japan-US Status of Forces Agreement, which stipulates how US military personnel are dealt with in Japan and is widely seen to legally favor the United States.

"The anger of the Okinawa people has reached the peak, with such incidents happening again and again. We can never put up with the air bases. US air bases not only in Okinawa but in other places of Japan shall all be scrapped," said a protester.

Okinawa hosts some 75 percent of US bases in Japan, yet the tiny sub-tropical island accounts for less than 1 percent of the country's total land mass, with local citizens becoming increasingly irate at their base-hosting burdens and the central government's ongoing pandering to the US requests, amid rising instances of crime, noise and pollution connected to the bases.

Criminal cases involving US military men repeatedly happened in Okinawa. A US Navy sailor was arrested in March after raping a woman in a hotel in Naha City, the capital of Okinawa. In 1995, an elementary schoolgirl was savagely gang-raped by three US servicemen.

The US president is here for the Group of Seven (G7) leaders' summit that is set to kick off Thursday.

The two sides also discussed agendas of the upcoming G7 summit, as well as other bilateral and regional issues, according to the press conference.

Obama is also planning to make an historic visit to the city of Hiroshima that was obliterated by a US atomic bomb during WWII on Friday after the G7 summit concludes, which will mark the first such visit by a sitting US president.