TOKYO, JAPAN - Japan's gaffe-prone prime minister, Taro Aso, apologised yet again on Thursday after criticising ailing elderly people for not staying healthy, a comment that could offend many in the world's most rapidly ageing country.

In the space of a couple of weeks, the 68-year-old Aso has offended doctors and parents of small children and upset various factions in his own party with a string of verbal blunders that have left some analysts wondering about his grip on power .

Commenting on Japan's ballooning medical costs, Aso told the government's top economic advisory panel that he tried to stay healthy by taking a daily walk, and asked why his tax payments should go to fund medical care for others who were more lax.

"My medical expenses are a lot lower because I walk and so on," said Aso, who comes from a wealthy family. "Why should I have to pay for those who just eat and drink and make no effort?"

Aso added that incentives should be introduced for those who maintain a healthy lifestyle.

He later apologised. "If I hurt the feelings of anyone who is ill now, I am sorry," the prime minister told reporters on Thursday. He added that he had been trying to explain that preventive medicine would help control medical costs.

Aso's top aide, Chief Cabinet Secretary Takeo Kawamura, told a news conference on Thursday that the prime minister had wanted to stress a need for self-help efforts to maintain health and had not intended to criticise sick people or Japan's medical system.

Kawamura, however, added: "If his comments hurt any feelings, maybe they were insufficient. But I would like to say that was not his intention."

Asked how he feels about being asked repeatedly to explain Aso's comments in recent weeks, Kawamura gave a bitter smile and said: "It would be better if I did not have to explain them.

"But it's part of his character and there may be various comments from now on, and it is my job to make efforts to let everyone understand his real intention."

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Aso's junior coalition partner called on him to watch his words, while ruling party lawmaker Taku Yamasaki said Aso should keep in mind a well-known proverb: "Silence is golden".

Just over a week ago, Aso was forced to apologise after accusing doctors, an important political interest group, of lacking common sense. Last year he was criticised for joking about Alzheimer's disease.

Aso had been expected to call a snap election after taking office in September following the sudden resignation of his predecessor, Yasuo Fukuda.

But the fallout from the world financial crisis and his party's weak performance in opinion polls have delayed the poll.