The United States has sounded out Japan on the idea of transferring about 1,500 U.S. marines based in Okinawa Prefecture to Iwakuni air base in Yamaguchi Prefecture as part of a broader plan to review the realignment plan for U.S. forces, sources close to Japan-U.S. relations said Monday.

Those 1,500 marines represent nearly half of the 3,300 or so Okinawa marines that Washington is considering moving to other Pacific areas instead of Guam — the sole destination for transferring around 8,000 Okinawa marines under a 2006 bilateral accord, the sources said.

The U.S. government has proposed relocating about 4,700 marines from Okinawa to Guam, about 1,500 to Marine Corps Air Station Iwakuni, and the remaining 1,800 to other places in the Asia-Pacific region, such as Hawaii and Australia, the sources said.