The United States is to shift 9,000 Marines out of Japan in a move Washington hopes will ease sometimes fractious relations with its ally over the huge American military presence.

The redeployment, which will see troops moved to Guam, Hawaii and Australia, will go ahead regardless of any progress on the moving of a busy airbase on Okinawa that had originally been a key condition set by the United States.

In a joint statement issued in Washington and Tokyo, the two sides said they remained committed to the relocation of the Futenma base from its present urban location to a coastal spot -- a move that is heavily resisted in Okinawa.

The two governments "reconfirmed their view that (this) remains the only viable solution that has been identified to date," the statement said.