Marine MV-22 Osprey aircrafts at Air Station Futenma in Ginowan on Okinawa Island in 2015. (Hitoshi Maeshiro/EPA)

The new U.S. ambassador to Japan, William Hagerty, embarked Monday on a careful visit to Okinawa, where he met with the governor who wants the American military presence on the southern island prefecture sharply reduced.

The U.S. bases on Okinawa are the most sensitive aspect of the two countries' security alliance, which President Trump and Japanese Prime Minister Shinzo Abe celebrated during their meetings in Tokyo last week.

The governor of Okinawa, Takeshi Onaga, has been campaigning against the relocation of the huge Marine air station at Futenma, in the middle of Okinawa's main island, to a remote spot on reclaimed land farther north at Henoko.

Hagerty is scheduled to visit Camp Schwab, the existing American base at Henoko, by helicopter Tuesday if the weather permits.

But Onaga and a majority of Okinawans, according to polls, don't want the base moved there. Instead, they want the base moved out the prefecture entirely, saying that the southern islands bear too much of the burden for the U.S.-Japanese alliance.

"People in Okinawa prefecture are working hard to stop that base ever being finished," Onaga told Hagerty during their 35-minute meeting, according to local media reports.

Onaga's previous attempts to persuade policymakers in Washington have led nowhere, with American officials telling him it is a matter for him to sort out with the central government in Tokyo. Abe's government has been pressing ahead with the plans to expand the base in Henoko, while Onaga has come up with creative ways to stymie them.

Onaga took the opportunity to make his case to Hagerty, complaining about the environmental impact of the construction at Henoko, particularly on sea life, and asking why Okinawa had to have the new base. 

Okinawa was occupied by the United States for almost three decades after the end of World War II, and the bases remained after it was handed back to Japan in 1972. The island chain accounts for less than 1 percent of Japan's landmass but houses 74 percent of the U.S. military bases in Japan.

"This is discrimination against Okinawa," Onaga told Hagerty.

In response, Hagerty said that the United States had an agreement to reduce the military burden on Okinawa and alleviate some of the impact of hosting the bases.

The governor also raised concerns about a recent series of military accidents in Okinawa involving tilt-rotor Ospreys or other military aircraft.

A Marine CH-53E transport helicopter last month caught fire in midair during a training flight in the northern part of Okinawa's main island. The copter crashed just 300 yards from houses. No one was injured.

Sporadic and sometimes serious crimes also have fueled Okinawans' concerns about the large American military presence.

A U.S. military contractor, Kenneth Franklin Shinzato, is expected to plead guilty Thursday to charges of raping a 20-year-old Okinawa woman last year and then dumping her body, but not guilty to killing her. 

Hagerty, a Tennessee businessman who spent three years working in Japan for the Boston Consulting Group earlier in his career, was at pains to be diplomatic at the start of his visit Monday.

"My visit to the Peace Memorial Park and Museum was a deeply moving experience," Hagerty wrote on Twitter after visiting the memorial to the 200,000-plus people who were killed during the three-month-long Battle of Okinawa in 1945. It was the only battle of World War II that was fought on Japanese territory.

Hagerty also visited Shuri Castle, the center of the kingdom that ruled the islands before Japan took them over, and tweeted that he had a "fantastic" visit with high school students.

This is not Hagerty's first visit to Okinawa since taking up his post at the end of August.

He and his family went to the main island in October, but the ambassador did not meet Onaga at that time. Analysts said that the sensitive spot was a strange choice for a family getaway, especially just weeks before snap parliamentary election in Japan. 

Still, Okinawans will likely feel encouraged that Hagerty has started his posting by showing an interest to their prefecture.

Caroline Kennedy, the U.S. ambassador before Hagerty, visited the islands during her term but met the governor only when Onaga's pro-base predecessor was in office.

Yuki Oda contributed to this report.

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