A government spokesperson has said Tokyo may reconsider re-examining a 20-year-old study after Japan backtracked on a landmark apology over forced prostitution during the Second World War.
Yoshihide Suga, the chief cabinet secretary, was responding to an ultra-conservative opposition lawmaker who sparked criticism when he claimed that sex slavery during the war was a myth.
Japan Restoration Party lawmaker Hiroshi Yamada said that Japanese children could not be proud of their country because of other "false" accusations.
More than 200,000 women of Korean, Chinese and Philippines origin were forced into sex slavery and trafficking by the Japanese military. The prostitution corps exploited so-called comfort women from across Japanese-occupied countries as well as a small number from Holland and Australia.
Women were abducted from their homes in countries under Japanese control. Some were lured by the promise of work, before they were incarcerated in the "comfort stations".
Suga said Japan might consider revising its views on the testimonies of 16 South Korean women who said they had been forced into prostitution by the Japanese military.
Suga's comments followed a statement by the deputy chief cabinet secretary at the time of the apology, Nobuo Ishihara, that Japan had never verified the 16 women's accounts.
The interviews were conducted by Japanese government officials in Seoul at the request of South Korea's government and were key to Japan's 1993 statement and apology later that year.
The statement, issued by then-chief cabinet secretary Yohei Kono, acknowledged many women were forced into prostitution for Japanese troops despite a lack of records clearly showing Japanese government involvement.
In 1994, the Japanese government set up the Asian Women's Fund to distribute additional compensation to comfort women from South Korea, the Phillipines, Indonesia, Taiwan and the Netherlands.
However, in 2007, the Japanese cabinet decided: "No evidence was found that the Japanese army or the military officials seized the women by force." The fund was dissolved.
US president Barack Obama recently urged the Japanese government to apologise for the use of comfort women during World War II. He called on Tokyo to "formally acknowledge, apologise and accept historical responsibility in a clear and unequivocal manner".
Japanese prime minister Shinzo Abe was urged to apologise publicly and for leading Japanese political figures to "refute claims denying the existence and purpose of the system as well as to educate current and future generations about this horrible wartime crime".
In May 2013, Toru Hashimoto, the mayor of Osaka, was forced to apologise for saying that forced prostitution was a military necessaity for his country's army during the war. Two former South Korean sex slaves demanded his resignation as a result.