Japanese voters in a city on Okinawa island elected a mayor Sunday who opposes plans for a controversial new US air base, complicating a row with Washington over relocating troops.

Two candidates in Nago city were squaring off over whether or not to give local support to a plan -- currently under review by the centre-left national government -- to build a major new Marine Corps air base there.

Susumu Inamine, 64, who campaigned on a platform of rejecting the base, ousted Yoshikazu Shimabukuro, 63, with a more-than 1,500-strong majority.

Official figures showed nearly 77 percent turnout by the city's 45,000 voters.

"I've run this election campaign with the pledge of not to build a base" in the coastal area of Nago city, Inamone told more than a hundred of his supporters who shouted and applauded in rapture. "I'll keep to this campaign promise with firm conviction," he said.

Prime Minister Yukio Hatoyama has said he may scrap an agreement with Washington to relocate the base from its current site in a crowded urban area of Okinawa to a quieter coastal site in the Nago area by 2014.

The issue has strained ties between Tokyo and Washington, which marked the 50th anniversary of their security pact last Tuesday, since Japan's new leaders took power four months ago ending a half-century of conservative rule.

The southern island of Okinawa, which saw some of the bloodiest battles of World War II, hosts more than half of the 47,000 US troops in Japan.

While some local businesses benefit from the heavy American military presence, many residents have long opposed it, citing crimes committed by servicemen as well as noise, pollution and the threat of accidents.

Hatoyama, whose coalition government includes pacifist groups and stern opponents of the US military presence, has said he will make a decision by May on where to move the controversial Futenma air base.

Some analysts have speculated that Hatoyama will ultimately settle with the current plan as there is no other realistic option for the replacement base in Japan, with no other communities willing to host it.

Even though the central government can technically overrule a local government decision to refuse the base, such a move could provoke sharp criticism as Hatoyama has vowed to consider "pains inflicted on Okinawans" and to respect local governments' decisions.

"The cabinet should respond to the will of residents," Mizuho Fukushima, the leader of the Socialists, the junior coalition partner of Hatoyama's Democratic Party, told reporters, Jiji Press reported.

Some observers have voiced frustration with the premier for making at times contradictory statements on the issue, leaving both Okinawans and Washington officials confused about his intentions.

"What Mr Hatoyama has said so far is inconsistent, and I don't know how he wants to settle the base row," said Yoshinobu Yamamoto, professor of international politics at Aoyama Gakuin University.

Yamamoto pointed out that, as an opposition politician years ago, Hatoyama advocated the withdrawal of all permanent US forces from Japan.

Hatoyama last month said that his views had changed but added that "there is an argument about whether it is appropriate to have foreign troops stationed in Japan if you think about the future, 50 or 100 years from now."

Yamamoto said: "If he truly believes in an 'alliance without the permanent presence of US troops' in Japan, there may be fundamental differences in the perception of the alliance between him and the United States.

"It could be a disaster for the future of the alliance."