TOKYO: Despite dwindling popular support for him amid a corruption scandal, Japan's opposition leader Ichiro Ozawa, vowed Wednesday to claim power in a general election to be held by September.

Ozawa, who heads the main opposition Democratic Party of Japan (DPJ), told a May Day rally in Tokyo, "We will win no matter how and bring about a change in government.

The rally, organised by Japan's biggest labour confederation, Rengo, was brought forward this year to coincide with a public holiday.

"We must create a strong government by winning the confidence of people as soon as possible," the 66-year-old told a crowd of 36,000 people.

The DPJ had led Prime Minister Taro Aso's ruling Liberal Democratic Party (LDP) in media polls until Ozawa became embroiled in the corruption scandal.

Ozawa's top aide, Takanori Okubo, was indicted a month ago for accepting donations through front groups from a construction company, a practice deemed illegal under a law on political funds.

Following the scandal, Aso's approval rating improved while Ozawa has had to resist pressure to quit, from both within and without his party.

The general election must be held before mid-September, when the term of the lower house expires.

A results of a telephone poll released by the Kyodo news agency Wednesday showed that the approval rating for Aso's government improved by 5.9 points in a month to 29.6 percent. A polls with similar results was published by other media this week.

Aso's disapproval rating fell 7.3 points to 56.2 percent, according to the poll, which drew valid responses from 1,014 people earlier this week, Kyodo said.

The poll showed that 65.5 percent of respondents wanted Ozawa to step down because of the scandal, compared with 66.6 percent in the previous survey.

It said 39.8 percent preferred Aso over Ozawa as prime minister, up 6.7 points from the March poll. In contrast, 26.1 percent chose Ozawa over Aso.

But Ozawa's party received support from 29.7 percent, compared with 29.4 percent for Aso's ruling conservative party.

The poll also showed 55.0 percent did not expect much from a 14.7 trillion yen (150 billion dollar) extra budget to finance government stimulus measures.

The budget, aimed at helping Japan out of recession in the midst of the global economic crisis, was submitted by the government to parliament Monday.

Ozawa pointed out that the extra budget would be covered by more than 10 trillion yen in government bonds and further upset the country's finances.

"It is an ultimate measure that will destroy the livelihood of people and ruin the country," he told the rally. "The Aso government is so irresponsible that it has no means and determination to help the country overcome the crisis."