Toru Hashimoto, the populist mayor of Osaka, also said American soldiers stationed in Okinawa should make more use of the island’s adult entertainment industry, which he said would reduce the incidence of sexual crimes against local women. Lawmakers and human rights groups swiftly condemned the remarks. So did South Korea, whose citizens made up the bulk of the so-called comfort women who served Japanese soldiers in military brothels. South Korea’s Yonhap News quoted a senior government official there as saying Mr. Hashimoto’s comments exposed “a serious lack of historical understanding and a lack of respect for human rights.” The conduct of the Japanese military in Asia before and during World War II remains a highly charged topic between Japan’s neighbors, who say Tokyo has not properly atoned for its history of wartime atrocities, and those, like Mr. Hashimoto, who feel that Japan has been unfairly demonized. Some historians estimate that 200,000 women were rounded up from across Asia to work as comfort women for the Japanese Army. Other historians put that number in the tens of thousands, and say they served of their own will. Japan formally apologized to the comfort women in 1993. Mr. Hashimoto told reporters in Osaka on Monday that they had served a useful purpose. “When soldiers are risking their lives by running through storms of bullets, and you want to give these emotionally charged soldiers a rest somewhere, it’s clear that you need a comfort women system,” he said. When pressed later, he insisted that brothels “were necessary at the time to maintain discipline in the army.” Other countries’ militaries used prostitutes, too, he said, and added that in any case there was no proof that the Japanese authorities had forced women into servitude. Instead, he put the women’s experiences down to “the tragedy of war,” and said surviving comfort women now deserved kindness from Japan. Mr. Hashimoto is a co-leader of the Japan Restoration Association, a populist party with 57 lawmakers in Parliament. His comments followed those of a string of Japanese politicians who have recently challenged what they say is a distorted view of Japan’s wartime history. Last month, Prime Minister Shinzo Abe seemed to question whether Japan was the aggressor during the war, saying the definition of “invasion” was relative. Mr. Abe’s comments heightened fears that he might seek to revise or even repudiate apologies that Japan has made to victims of its wartime conduct. The 1993 apology to comfort women and another in 1995 to nations that suffered from Japanese aggression during the war have been condemned by Japanese ultranationalists. Mr. Hashimoto’s remarks swiftly drew widespread public rebuke. “The comfort women system was not necessary,” said Banri Kaieda, president of the opposition Democratic Party. That Japan was the clear aggressor in war “is a fact we must face up to,” he said. Mr. Hashimoto also said Monday that he had told a senior American military official at the Marine Corps base in Okinawa that United States soldiers should make more use of the local adult entertainment industry to reduce sexual crimes against local women. “We can’t control the sexual energy of these brave marines,” Mr. Hashimoto said he had told the American officer, whom he did not identify, on a recent visit there. “They must make more use of adult entertainers.” Early Tuesday, Mr. Hashimoto took to Twitter, on which he has over a million followers, to suggest that the United States was no better than Japan because prostitution is rife around American bases. He also argued that by banning troops from all forms of adult entertainment in Japan, the United States military was discriminating against women legally working in that business. In a comment posted on its Web site, the Women’s Action Network, which advocates for women’s rights in Japan, called Mr. Hashimoto’s earlier comments “shocking.”