Japan Restoration Party deputy leader and Osaka Mayor Toru Hashimoto attends a joint news conference to unveil their party's election campaign platform in Tokyo, in this November 29, 2012 file photo.
The United States condemned as "outrageous and offensive" comments by the mayor of the Japanese city of Osaka who said this week that Japan's military brothels during World War Two were "necessary" to provide respite for soldiers.
The remarks by Osaka Mayor Toru Hashimoto drew strong criticism from China and South Korea, two nations sensitive to what they see as any attempt to excuse Japanese abuses before and during the war.
Historians estimate that as many as 200,000 sex slaves, known as comfort women, were forced into submission in the Imperial Japanese Army's brothels during the war.
"Mayor Hashimoto's comments were outrageous and offensive," said State Department spokeswoman Jen Psaki.
"What happened in that era to these women who were trafficked for sexual purposes is deplorable and clearly a grave human rights violation of enormous proportions," she said, adding that Washington hoped Japan would work with its neighbors to address the mistakes of the past.
The Japanese government has sought to distance itself from Hashimoto's comments.
"The government's stance is, as we have said before, that we feel great heartache when we think about the indescribable suffering of those who experienced this," Japan's Chief Cabinet Secretary Yoshihide Suga said, although he declined to comment directly on Hashimoto's remarks.