Gov. Hirokazu Nakaima approved the Japanese Defense Ministry's application to reclaim land for the base on Okinawa's coast to replace the U.S. Marine Corps base in Futenma, a more congested part of Okinawa's main island.
But he later told a news conference that he would continue pressing to move the Futenma troops off Okinawa entirely, noting estimates it would take 9 1/2 years to build the base.
"My thinking remains it would be fastest to relocate outside (Okinawa) prefecture to a place where there is already an airport," he said.
He added that he approved the land reclamation because it met all environmental requirements.
The debate over the future of Futenma dates to 1996, when the U.S and Japan signed an agreement to close the base and move its operations elsewhere in Okinawa. In 2006, the two countries agreed to relocate the base to a relatively unpopulated area called Henoko in Nago city. But after the Democratic Party of Japan took power in 2009, it raised the possibility that the base could be moved off of Okinawa. While it later agreed to the Henoko plan, the proposal energized a movement to move the base elsewhere.
About half of the 50,000 American troops in Japan are based in Okinawa, and many residents complain about base-related crime, noise and the risk of accidents. Some feel the island is bearing an unfair share of the burden of protecting Japan from attack.
A key factor could be the outcome of a mayoral election in Nago next month that pits an opponent of the Henoko plan against a supporter.
"The governor is taking a risk putting the prestige of his office behind the project," said Jun Okumura, a political analyst and former national government official. "I still don't see the project going forward without the consent of the Nago mayor, but I see that this improves the chances of success."
Nakaima's decision could face court challenges and protests.
"What the governor has done is unforgivable," said Yuichi Higa, the head of the Nago assembly. "Residents who are opposed will surely resort to the use of force, such as blocking roads to stop this from happening."
Hiroshi Ashitomi, head of an opposition group in Nago, said his group would file a lawsuit seeking to cancel the governor's approval of the land reclamation.
The decision was a politically difficult one, and came only after Japanese Prime Minister Shinzo Abe met with Nakaima in Tokyo on Wednesday and offered him a package that included pledges of increased financial assistance for Okinawa.
While the base consolidation plan is designed to reduce the impact of the U.S. military on Okinawa, opponents want the Futenma base moved off Okinawa completely. The new base is part of an agreement that would also move 9,000 Marines off Okinawa, including transferring 5,000 to Guam.
The U.S., which wants to move forward with its plans to redeploy troops in Asia, welcomed the governor's decision. "The U.S. looks forward to working with the government of Japan toward base consolidation," the U.S. Embassy in Tokyo said in a statement.
Associated Press writers Yuriko Nagano and Emily Wang contributed to this report.
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