TOKYO/OKINAWA - Japan's prime minister said Tuesday that it will be impossible to move all parts of a key US Marine base out of Okinawa, breaking with past promises to relocate the facility outside the southern island.

It was the first time since Yukio Hatoyama became prime minister in September that he officially acknowledged that at least part of Futenma US Marine Corps airfield would remain in Okinawa, which hosts more than half the 47,000 American troops based in Japan under a security pact.

He urged Okinawans to accept a plan to keep at least part of the controversial US base on the island, risking a further blow to voter support ahead of an election.