Japan's Supreme Court is expected to hand down a ruling against Okinawa Prefecture over a landfill project to relocate a US military facility within the prefecture.

The central government began reclamation work in a coastal area of the Henoko district in Nago City in 2018 to relocate the Futenma air station to the less-populated area. But about 70 percent of the reclamation site was found to be soft ground.

The government sought a revision to the original plan to solidify the soft ground so that the land there can be reclaimed.

But the Okinawa prefectural government refused to approve the revision, putting a halt to the reclamation work.

Last year, the land ministry issued a directive, demanding that the Okinawa government acknowledge the revision. In response, the prefecture filed a suit demanding that the government withdraw the instruction.

In March, the Fukuoka High Court's Naha branch ruled against the prefecture, saying that the central government's involvement was legitimate. Okinawa appealed to the Supreme Court.

Presiding judge Oka Masaaki at the Supreme Court says that he decided to hand down a decision on September 4.

The high court decision that ruled against the prefecture is expected to be upheld as hearings necessary to overturn the decision will not be held.

If upheld, the prefecture will be obliged to approve the work to solidify the soft ground, or the central government can give the go ahead for carrying out the work on behalf of the prefecture even if the local government does not comply with its instruction.

The central government and Okinawa have engaged in a fierce tug of war with 13 lawsuits over the government's plan to relocate the US air base to Henoko.

Planned work to solidify the soft foundation at the site for land reclamation has been one of major pillars of the project.

The first decision by the Supreme Court on the matter could affect other related court cases and relocation works.