The Japanese military's forced prostitution of Asian women before and during World War II was necessary to "maintain discipline" in the ranks and provide rest for soldiers, an outspoken nationalist mayor has said.

The comments made on Monday are already raising anger in neighbouring countries that bore the brunt of Japan's wartime aggression, and that have long complained that Japan has failed to make amends for wartime atrocities.

Toru Hashimoto, the young, brash mayor of Osaka who is also co-leader of an emerging conservative political party, also told reporters that there was not clear evidence that the Japanese military coerced women to become what are euphemistically called "comfort women".

"To maintain discipline in the military, it must have been necessary at that time," said Hashimoto. "For soldiers who risked their lives in circumstances where bullets are flying around like rain and wind, if you want them to get some rest, a comfort women system was necessary. That's clear to anyone."

Historians say up to 200,000 women, mainly from the Korean Peninsula and China, were forced to provide sex for Japanese soldiers in military brothels.

In South Korea's capital Seoul, the foreign ministry expressed disappointment over what it called a senior Japanese official's serious lack of historical understanding and respect for women's rights.

It asked Japan's leadership figures to look back on their country's imperial past, including grave human rights violations that were committed, and correct their anachronistic historical views.

'Indignant comments' 

China's foreign ministry criticised the mayor's comments and saw them as further evidence of a rightward drift in Japanese politics under Prime Minister Shinzo Abe.

"We are appalled and indignant about the Japanese politician's comments boldly challenging humanity and historical justice,'' Hong Lei, the ministry's spokesman, said at a daily media briefing.

"The way they treat the past will determine the way Japan walks toward the future. On what choice Japan will make, the Asian neighbors and the international community will wait and see."

Asked about a photo of Abe in a fighter jet with the number 731, the number of a notorious, secret Japanese unit that performed chemical and biological experiments on Chinese in World War II, Hong again urged Japan not to whitewash history so as to improve relations with countries that suffered under Japanese occupation.

"There is a mountain of definitive iron-hard evidence for the crimes they committed in the Second World War. We hope Japan will face and contemplate their history of aggression and treat it correctly,'' Hong said.

Chinese protesters who said they performed hard labour in Japan in the War have demanded apologies [AFP]

Abe posed, thumbs up, in the aircraft during a weekend visit to northeastern Japan.

Last week, Japan acknowledged that it conducted only a limited investigation before claiming there was no official evidence that its imperial troops coerced women into sexual slavery before and during World War II.

A parliamentary statement signed by Prime Minister Shinzo Abe last Tuesday said that the government had a set of documents produced by a postwar international military tribunal containing testimony by Japanese soldiers about abducting Chinese women as military sex slaves.

That evidence apparently was not included in Japan's only investigation of the issue, in 1991-1993.

Tuesday's parliamentary statement also said documents showing forcible sex slavery may still exist. The statement did not say whether the government plans to consider the documents as evidence showing that troops had coerced women into sexual slavery.

Source: Agencies