Japan said Monday the United States had returned a sliver of land at a controversial US air base on the southern island of Okinawa which has sparked a lengthy and fierce dispute.

Tokyo said the return of the land, which accounts for less than one percent of the 481-hectare (1,188-acre) Futenma base, would improve conditions for locals.

But many Okinawa residents want the Marine air base moved off their island altogether.

They reject the Japanese and US government project to minimise noise and potential safety problems by moving the base from a crowded city to a sparsely populated district in Okinawa's north.

Both Tokyo and Washington have consistently rejected the idea of moving the base out of Okinawa altogether.

The US gave back the plot under a 2015 agreement to speed up the return of land on the island.

"Thanks to the return of the land, a city road will be fully open and the living environment for locals will be largely improved," Chief Cabinet Secretary Yoshihide Suga, the government's top spokesman, told reporters.

"We'll try to visibly reduce Okinawa's burden," he said.

In February the government resumed work on building the replacement base after it was stalled by a series of administrative and legal moves, sparking angry protests and scuffles with police.

Okinawan Governor Takeshi Onaga had tried to block efforts to reclaim land for the new offshore facility and he and Prime Minister Shinzo Abe filed rival lawsuits to try to settle the issue.

But in December the Supreme Court ruled in favor of the central government, giving the green light to move ahead on construction.

Onaga, however, filed a fresh lawsuit last week against the central government to try and halt construction.

The governor had no immediate comment on the land return.

Okinawa, which accounts for less than one percent of Japan's total land area, hosts about 28,000 US troops -- more than half of about 47,000 American military personnel stationed in Japan.

Islanders have complained for decades that the rest of the country ignores their burden, which also includes hosting some 70 percent of land allotted for US bases in Japan.

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