Japan and the United States are considering downsizing a planned military-civilian airport off Nago, Okinawa Prefecture, for relocating the U.S. Marine Corps Futenma Air Station in Ginowan, sources close to bilateral relations said Thursday.

But the prefecture may not agree because a scaled down airport would not be able to accommodate commercial aircraft, a condition Okinawa set in exchange for approving the original relocation plan. The Futenma base is mainly for helicopters.

The plan would involve trimming the offshore runway off Nago's Henoko district to about 1,300 meters from the initially planned 2,000 meters. If the two countries can officially agree, Tokyo hopes to obtain consent from the prefecture by year's end, the sources said.