Japan and the US vowed Friday to press ahead with the construction of a new air base on strategic Okinawa, and pledged to speed up the return of some land on the island where pacifist sentiment runs high.

The announcement came just two days after Tokyo pressured Okinawa in court to try and force its governor to support the controversial transfer of a US Marine air base from one part of the island to another.

Takeshi Onaga, the governor, opposes the move and argues that the rest of Japan needs to share the burden of supporting the country's decades-long security alliance with close ally the United States.

He wants the unpopular Futenma air base, located in a crowded urban area and widely seen as dangerous to residents, to move off the island entirely rather than to a more remote and environmentally delicate part as pushed for nearly 20 years by Tokyo and Washington.

US Ambassador to Japan Caroline Kennedy said Friday that Washington backed the existing relocation scheme, and argued that the planned return of US base properties to Okinawa should ease its burden.

"The US government remains committed to executing this entire plan at the earliest possible date," she said in a joint announcement with Japan's Chief Cabinet Secretary Yoshihide Suga.

"We look forward to working with the government of Japan to make that happen."

Under the announced deal, some sections of land now used by US forces, including on Futenma, will be returned to Okinawa as early as in fiscal year 2017, which Japan's top-selling Yomiuri Shimbun reported was at least five years ahead of an earlier timeline.

But the land covered under the announcement accounts for less than one percent of the Futenma facility, Kyodo News said.

Suga, meanwhile, emphasised the importance of "our alliance being further strengthened through steady implementation" of the base relocation deal

The Japanese government and Okinawa fought in an initial court hearing Wednesday where Tokyo is suing to reverse Onaga's decision to stop the government from building the new US base.

Okinawa, the site of a bloody World War II battle between Japan and the US, is considered a strategic linchpin for the countries as they face China's increasing military might and the regional threat of North Korean missiles.

Okinawa, which makes up less than one percent of Japan's total land area, is home to about 75 percent of US military bases in the country and more than half of the 47,000 American military personnel stationed in the country.

Residents have complained for decades about noise, crimes, accidents and other problems associated with the American military presence.