The government on Tuesday began building sea walls around a planned replacement facility for the U.S. Air Station Futenma in Okinawa Prefecture, taking another step forward with the controversial relocation plan.

Despite persistent local opposition to the relocation of the base from residential Ginowan to the coastal area in Nago, the state is moving ahead with construction —dumping building materials into the sea and planning to launch full-fledged landfill work inside the sea walls in the first half of next year. The prefecture wants the base moved out of Okinawa altogether.

"I'm convinced that the start of the construction marks a steady first step toward realizing the complete return of the Futenma airfield," Defense Minister Tomomi Inada said in a statement, referring to a U.S.-Japan agreement on the return of the land occupied by the base to Japan.