Japan's government is seeking an early conclusion of a trial over a landfill project for moving a US military base in the southern prefecture of Okinawa.

The government plans to move the US Marine Corps Futenma Air Station from the densely populated city of Ginowan to an offshore site at Henoko in Nago City.

But the ground at the reclamation site was found to be too soft.

The government then applied for permission from the prefecture to revise the original reclamation plan and carry out reinforcement work.

The prefecture, which opposes construction of a new US base, refused to approve the revision.

Last month, the Supreme Court turned down Okinawa's appeal of a high court decision upholding the central government's directive for the prefecture to approve changes to the reclamation plan.

The top court ruling obliges Okinawa to give permission in line with the central government's instructions.

But Okinawa Governor Tamaki Denny on Wednesday told the central government it would be difficult to give his approval by the deadline.

On Thursday, the central government asked the Naha branch of the Fukuoka High Court to order Okinawa to approve the revised project.

The government explained the details of its complaint on Friday.

It argues that the prefecture has neglected a directive issued by the land minister in April last year demanding that the prefecture acknowledge the revision.

Tokyo also argues that delaying the landfill project would clearly affect important issues, including national security and how to avoid making the Futenma base permanent. It says a delay would significantly undermine the public benefit.

The government maintains that such circumstances meet the criteria for execution by proxy under the local autonomy act. It also says more than three years have passed since it applied for a revision to the original plan.

The government says a court hearing should be held by October 20 and the trial concluded that day so the court can promptly hand down a ruling ordering Okinawa to approve the revision.

The government is asking Okinawa to do so within three days after it receives the ruling.

Governor Tamaki said on Thursday that he will consider what pleas he can make after he receives the central government's complaint.