The United States plans to return to Japan roughly half of a large U.S. military training area in Okinawa on Dec. 22, a Japanese government source said Thursday.

The return of land within the U.S. military's Northern Training Area in the villages of Kunigami and Higashi would mark the largest return of land used as a U.S. base there since the 1972 reversion of Okinawa to Japan from U.S. control.

It would reduce the acreage occupied by U.S. military facilities in Okinawa by 17 percent, shrinking the prefecture's burden from hosting 74 percent of all U.S. military facilities in Japan to 70 percent in terms of land area.