GINOWAN, Japan — Thousands were expected to rally Sunday against a US military base on Japan's Okinawa island, raising the heat in a simmering row days before President Barack Obama visits Tokyo.
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".
But the rise of a new centre-left government in Tokyo in September, ending decades of conservative rule, has brought the issue to the centre of national politics and strained Japan's most important security alliance.
More than 30,000 protesters were expected to gather from 0500 GMT in a park near the controversial US Marine Corps Futenma Air Base in Ginowan city, organisers said. Obama visits Japan on Friday and Saturday.
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, Defense 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 (1,000 miles) south of Tokyo, saw some of the bloodiest battles of World War II.
American occupation forces only handed the island back to Japan in 1972, but it continues to host more than half of the 47,000 US troops in the country.
Washington and Tokyo have been close security allies in the post-war era, with the United States guaranteeing Japan's defence and providing nuclear deterrence during and after the Cold War.
Japan's post-war constitution bars its Self-Defence Forces from offensive military action and Japanese soldiers abroad, despite limited deployments in Iraq and on peace-keeping missions, have not fired a shot in anger since WWII.