Local opposition has often flared against the large US military presence on the southern island, strategically located within easy reach of China, Taiwan and North Korea and dubbed the United States′ "unsinkable aircraft carrier".

In a new development Japan′s foreign minister has said that Tokyo′s decision on relocating the US Marine Corps Futenma Air Base could be delayed till next year.

A string of local elections next year on the island could also sway the fate of the controversial military facility, Foreign Minister Katsuya Okada said.

"I think the end of December can be a point of time by which we should work out a rough plan... but it may be delayed from this," Okada told a talk show on the private Asahi network.

The government of Prime Minister Yukio Hatoyama, which swept to power in September, has said it may want the base, now located in a densely populated area, moved off the island or even out of the country.

The rise of a new centre-left government in Japan, ending decades of conservative rule, has brought the issue of the US military presence in the country back to the centre of national politics and has strained Japan′s most important security alliance.

The Futenma base, located in a densely populated urban area, has emerged as a flashpoint for local opponents who have been angered by aircraft noise, pollution, the risk of accidents and crimes committed by US service personnel.

Okinawans reacted with fury to the 1995 rape of a schoolgirl by three US servicemen, and demands to close the base on safety grounds grew when a US helicopter crashed into the front yard of a local university in 2004.

The government of Prime Minister Yukio Hatoyama, which swept to power in a landslide and has vowed a less subservient relationship with Washington, has said it may want the base moved off the island or even out of the country.

The United States has demanded Japan honour a 2006 agreement under which the Futenma base would be closed but its air operations moved to an alternative site to be built on Okinawa by 2014 in the coastal Camp Schwab area.

But activists near Camp Schwab also oppose the planned new base, which would be built on reclaimed land and would include two runways likely to affect a marine habitat home to corals and an endangered sea mammal, the dugong.

On a visit to Japan last month, Defence Secretary Robert Gates bluntly urged Tokyo to "move on" and resolve the issue before Obama′s arrival, stressing that Washington does not want to renegotiate a pact that was years in the making.

Hatoyama has said Japan will need more time to resolve the tricky question as it weighs the demands of Washington and of the people of Okinawa, a heartland of left-leaning and pacifist groups who oppose the bases.

Subtropical Okinawa, located about 1,600 kilometres south of Tokyo, saw some of the bloodiest battles of World War II.