TOKYO, JAPAN - OUTSPOKEN Japanese politician Taro Aso, has offended the main opposition party with a comment about Nazis, days after winning a senior post in the ruling party that could help him become prime minister.

Mr Aso, who missed out on becoming prime minister in a Liberal Democratic Party (LDP) leadership vote last year, is a frontrunner to win the top job if unpopular Prime Minister Yasuo Fukuda can not improve his voter ratings.

Upper house spokesman Satsuki Eda of the opposition Democrats told Mr Aso in a meeting that the electorate was shifting away from the LDP, the Nikkei financial daily and other papers said.

The Democrats said the comment was unforgiveable and urged Mr Aso to withdraw it, the Nikkei said. He later told reporters he was not comparing the Democratic Party to the Nazis.

An official from Mr Aso's office confirmed he had referred to Nazis but played down the significance of it.

'He was saying that the fact that debate has not been progressing in parliament is a serious problem and that the Nazi regime arose from a similar situation,' said the staff member, who declined to be identified.

The opposition parties have dominated the upper house of parliament since an election just over a year ago and have used their power to block government legislation.

Mr Aso has a history of making remarks that some consider offensive. In 2001, he said Japan should become the kind of country where 'rich Jews' would want to live.

He has also made comments appearing to defend Japan's 20th century colonisation of the Korean peninsula and joked about Alzheimer's disease, a sensitive topic in rapidly ageing Japan.

Mr Aso is one of Japan's most popular politicians. A poll published in the Sankei Shimbun on Tuesday showed 23 per cent of respondents would like him to be prime minister, compared with only 6.4 per cent who felt current premier Yasuo Fukuda was the best person for the job. -- REUTERS