There is growing concern that Japan may move soil from an area suspected to be where at least hundreds of Koreans were buried during Japan’s colonial era for the construction of a new U.S. air base in the Okinawa region.

Based on documents from Japan's Defense Ministry on Monday, Yonhap News Agency said Tokyo requested approval from the Okinawa prefecture government last April to change filling materials to be used in the construction.

The project involves relocating the U.S. Marine Corps Air Station Futenma south of Okinawa Island to Henoko Bay in the central area.

The document mentions bringing soil from the Okinawa city of Itoman and town of Yaese, where the bloody 1945 Battle of Okinawa took place, during which some 200-thousand Japanese and Americans are estimated to have died.

Over three-thousand-400 Koreans are believed to have been conscripted to fight for imperial Japan, and at least 700 of them are estimated to have died.

Takamatsu Gushiken, the head of a Japanese civic group involved in excavations for the remains of the war dead, has strongly protested the revisions, calling it an affront to the dignity of the war dead.