Japan's unpopular Prime Minister Yasuo Fukuda suffered a new blow as his party lost control of Okinawa's assembly, results showed Monday, emboldening the opposition, which is set to censure him.

The southern island held local elections on Sunday, with the opposition hammering away against a new health care plan for the elderly which has raised hackles in one of the world's greyest countries.

Fukuda's Liberal Democratic Party-led coalition won 22 seats, down from 27 in the prefecture's previous assembly. The opposition increased its strength from 20 to 26 seats, according to the Election Commission.

"We regard these results as the voice of voters nationwide. It was a vote in which the policies of the Fukuda cabinet were thrown into question," said Yukio Hatoyama, secretary general of the main opposition Democratic Party.

The opposition won one house of parliament in national elections last year, a breakthrough in a country where the Liberal Democrats have been in power for all but 10 months since 1955.

The opposition has threatened to use its power in the upper house to pass a censure motion against Fukuda's government. News reports said the opposition expected to present the motion on Wednesday.

But Fukuda has already said he will ignore the motion, which is non-binding. He has said he does not want political instability before Japan hosts the July 7-9 summit of the Group of Eight rich nations.

Instead, Fukuda is expected on Monday to unveil plans to force industry to curb carbon emissions blamed for global warming to help Japan meet its commitments under the Kyoto Protocol.

Such a plan will likely win Fukuda new credibility with environmentalists and the European Union although it has been resisted by some powerful businesses and bureaucrats in Japan.

The Okinawa vote could also cause new obstacles for the government's plan to relocate a major US air base within the island.

Okinawa is home to slightly more than half of the US troops in Japan.

The US military has agreed to move the Futenma Marine base, long a source of local grievances as it lies in a crowded urban area, to a more isolated location off a fishing village.

But the opposition has called for the base to be moved out of Okinawa entirely.

The United States plans to move 8,000 Marines from Okinawa to Guam, a US territory, by 2014.

Despite their poll setback an ally of the Liberal Democrats, Hirokazu Nakaima, remains governor of Okinawa, a position elected separately.

The controversial new medical plan, which took effect in April, deducts health care costs directly from pension payments for people aged 75 or older, leading to a flurry of complaints from the elderly, who fear their costs will rise.