Washington has welcomed Tokyo's formal request to Okinawa for permission to provide landfill for the U.S. Futenma replacement base, calling it "a key milestone" after years of tough bilateral negotiations.

"We welcomed the government of Japan's submission of the landfill permit request to the Okinawa Prefectural Government today," Pentagon press secretary George Little said in a statement Friday.

"This is a key milestone that comes after years of hard work between the United States and Japan," he said. "It marks a significant step toward realizing the vision of the 2006 realignment road map (for U.S. forces in Japan) and toward achieving a sustainable U.S. military presence with less impact on the Okinawan people.