Outspoken Osaka Mayor Toru Hashimoto said soldiers living with the daily threat of death needed some way to let off steam which was provided by the comfort women system.
Up to 200,000 women from Korea, China, the Philippines and elsewhere were forcibly drafted into brothels catering to the Japanese military in territories occupied by Japan during WWII, according to many mainstream historians.
"When soldiers risk their lives under a hail of bullets, and you want to give them a rest somewhere, it is clear that you need a comfort women system," Hashimoto said.
"There is worldwide recognition... That the issue of comfort women amounts to a wartime rape committed by Japan during its past imperial period in a serious breach of human rights," a Seoul foreign ministry spokesman told AFP.
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"Our government again urges Japan's prominent officials to show regret for atrocities committed during Japan's imperial period and to correct their anachronistic way of thinking and comments."
In Beijing, Foreign Ministry spokesman Hong Lei said China was "shocked and strongly infuriated" at the comments.
"How to deal with its past will decide how Japan can embrace the future."
Hashimoto, who is co-leader of the national Japan Restoration Party, acknowledged that some women providing sexual services to Japan's soldiers did so "against their will", something he attributed to "the tragedy of war".
But he said there was no evidence this had been officially sanctioned by the state and that the use of prostitutes by servicemen was not unique to Japan.
Japan's top government spokesman and Chief Cabinet Secretary Yoshihide Suga today refused to comment directly on Hashimoto's remarks.