Mr Taro Aso, 67, had reportedly made the remarks in a meeting with Upper House Speaker Satsuki Eda on Monday, the opposition Democratic Party of Japan (DPJ) said.

The Nikkei financial daily reported that when told the electorate was shifting away from the ruling party, an irritated Mr Aso replied: 'If you look at history, there is an example of regimes like the Nazis taking power as a result of people leaving the ruling party.'

DPJ secretary-general Yukio Hatoyama said the remarks could give people the impression that the party would behave like Nazis in power.

'This is not an issue that we can overlook. We will demand an apology,' he said.

Mr Aso yesterday argued that he did not mean to say the opposition favoured policies similar to the Nazis, though he did not offer a full retraction.

He told reporters he was referring to the political stalemate in Japan since the opposition won control of one House of Parliament last year.

'I was trying to explain that there have been many such cases in the past after parliamentary discussions were boycotted,' he said. 'There were similar cases before World War II, and that's what I used as an example.'

The DPJ took control of the Upper House in elections a year ago, and have used their position to block or delay legislation passed by the ruling coalition-dominated Lower House. They have also boycotted legislative action.

The ruling Liberal Democratic Party (LDP) has not released a precise quote of Mr Aso's comments during the meeting, but the party conceded that he urged the opposition to behave more responsibly in Parliament.

Mr Aso was named last Friday as the LDP secretary-general in a Cabinet reshuffle. He ran unsuccessfully last year for prime minister, and is widely considered the front runner to succeed the unpopular current Prime Minister, Mr Yasuo Fukuda.

A former diamond trader and Olympic marksman, Mr Aso is well-known for his abrasive comments.

He was forced to apologise in 2001 after saying that 'the best country in the world would be a country where the richest Jewish people would want to live'. And last year, he was forced to apologise for making a crack about the Alzheimer's disease in Japan, whose population is among the oldest in the world.

Still, he has earned popularity among voters with his straight talk. A poll published in the Sankei Shimbun yesterday showed 23 per cent of respondents would like him to be prime minister, compared with only 6.4 per cent who felt Mr Fukuda was the best person for the job.

REUTERS, ASSOCIATED PRESS, AGENCE FRANCE-PRESSE