THE Japanese military's forced prostitution of Asian women before and during the Second Word War was necessary to maintain discipline in the ranks and provide rest for soldiers who risked their lives, a politician has said.

Asian countries that bore the brunt of Japan's wartime aggression have said Japan has failed to fully atone for atrocities.

Osaka Mayor Toru Hashimoto, who is co-leader of an emerging conservative political party, said there was no clear evidence the Japanese military coerced women to become what are referred to as "comfort women".

He said: "To maintain discipline in the military, it must have been necessary at that time. 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.

An unidentified South Korean government official said it was disappointing that a senior Japanese official "made comments supportive of crimes against humanity and revealed a serious lack of a historical understanding and respect for women's rights".

Mr Hashimoto's comments come amid mounting criticism at the prospect of Prime Minister Shinzo Abe's conservative government revising Japan's past apologies for wartime atrocities.

Mr Abe has acknowledged "comfort women" existed but has denied they were coerced into prostitution.

Over the past two days, top officials in Mr Abe's government have appeared to ease their concern over Japan's past apologies, apparently to calm tensions with South Korea and China.