TOKYO — The mayor of one of Japan’s largest cities, who is seen by some as a possible future prime minister, drew an outcry on Monday after he said women forced into wartime brothels for the Japanese Army during World War II had served a necessary role in providing relief for war-crazed soldiers.

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.”