NHK has learned that, as early as Tuesday, the Japanese government will start the preparatory work that is needed to reinforce the ground at the site where a US military base will be relocated in Okinawa Prefecture.

The government plans to reclaim land off Henoko, which is located in Nago City. The US Marine Corps Futenma Air Station will be relocated to that site. The facility is currently located in the densely populated city of Ginowan.

The Okinawa prefectural government is opposed to the relocation plan. It has refused to give its approval for the work that must be done to reinforce the soft ground at the reclamation site on Oura Bay. But in December the central government won a court ruling, which allowed it to override the prefecture's objections.

Defense Ministry sources say the preparatory work that could begin on Tuesday includes the installation of a silt screen in the sea. This needs to be done, so that an offshore construction yard can be built. After that, seawalls can be developed.

Ministry sources say full-fledged work to construct the yard could begin as early as Friday.

The Defense Ministry says the ground improvement work will raise the total cost of the relocation project to about 930 billion yen, or about 6.5 billion dollars. That is 2.7 times higher than the initial estimate.

The ministry says it will be possible to transfer the base after all the construction work and other procedures have been completed. That will be in about 12 years.

Okinawa Prefecture is still urging the central government to abandon the plan to relocate the base. It is also calling on the central government to engage in dialogue, so a new solution can be found.