Tokyo - Japan's top opposition leader was facing increasing pressure to step down after his secretary was arrested for allegedly taking illegal corporate donations, Japanese media reported Monday.

Ichiro Ozawa, president of the Democratic Party, rebuffed mounting calls for his resignation within his own party even after Takanori Okubo, also an accountant for Ozawa's political group Rikuzankai, was arrested last week.

Japan's two largest newspapers said more than half the people surveyed wanted Ozawa to step down as the opposition leader.

The number of people who thought the 67-year-old veteran politician would be appropriate to govern the nation has declined over the scandal from 40 per cent to 35 per cent, the Yomiuri Shimbun survey showed Monday.

Meanwhile, the support rate for Prime Minister Taro Aso rose to 26 per cent from 24 per cent, the daily said.

The approval rate for Aso hit single digits before Ozawa became the centre of corporate-donation scandal. Calls for an early general election were increasing.

The Asahi Shimbun newspaper poll showed on Monday that 36 per cent surveyed said they would vote for the opposition leader for proportional representation seats for the lower house election, down from 42 per cent in February.

Japanese prosecutors said Okubo set up the amount of donations at about 25 million yen (254,550 dollars) to be offered near the end of a year after he made a prior arrangement with officials of Nishimatsu Construction Co, according to Jiji Press.

The two parties agreed on the arrangement for the first time around 2000, when Okubo took the post as an accountant, Jiji said. (dpa)