Exit polls from Sunday's Okinawa gubernatorial election pointed to a win by Onaga, just hours after US President Barack Obama agreed with the Japanese and Australian premiers, Shinzo Abe and Tony Abbott, to boost regional security.

Washington had sought their tripartite encounter as the G20 summit neared its close in Brisbane, Australia, to reassure allies about the United States' strategic shift toward the Asia-Pacific region.

Japan's relations with its neighbors China and Russia have been strained for years because of maritime territorial claims in the South China Sea.

Blow for Abe ahead of election

Japanese media said defeat for Okinawa's incumbent governor Hirokazu Nakaima, who was seeking a third term, would amount to a severe blow for Abe, just days before he is expected to call a snap general election.

Okinawa is home to more than half of the 47,000 US service personnel stationed in Japan, whose central government wants the current Futenma air base relocated 50 kilometers (30 miles) north of its current site, to remove it from a crowded urban area (pictured).

Onaga to block landfill

Onaga, a former mayor of Okinawa's capital Naha City, said on Sunday he would retract approval for landfill work at the proposed new site.

"I am determined to work toward cancelling and withdrawing it," he told the news agency Kyodo.

Onaga cited strong objections among Okinawa residents to plans to rebuild the base in what he termed their "beautiful Oura Bay." Recent opinion polls indicate that around 80 percent of resident oppose the planned move.

A local anti-base activist Takako Shinohara said the massive landfill project "would destroy the area's biodiversity" near Nago city in northern Okinawa.

Cash injection

Nakaima, who ran with backing of Abe's Liberal Democratic Party (LDP) had been criticized for accepting a central government cash injection pledge in exchange for reversing years of opposition to the project.

Tokyo and Washington first agreed to relocate Futenma, a base used by US Marines, to another site in 1996.

Some local opponents want the US military to leave Okinawa altogether.

Post-war US rule

Okinawa was annexed by Japan in the 19th century and was ruled by the US for almost three decades after World War II:

The current Futenma base, with its roaring aircraft engines, sits in a crowded residential area. Inhabitants recall the case of a 2004 crash of a military helicopter into the grounds of a local university.

ipj/pfd (Reuters, AFP, dpa)